Water-breakable formulations and additive manufacturing processes employing same

ABSTRACT

Curable formulations which form cured materials that are breakable upon immersion in water are disclosed. The cured materials break into a plurality of particles being a few millimeters or less in size. Methods of fabricating three-dimensional objects utilizing the curable formulations are also disclosed, as well as model objects fabricated thereby. The curable formulations include at least a mono-functional curable material and a multi-functional curable material, as described in the specification.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to additivemanufacturing (AM), and more particularly, but not exclusively, towater-breakable formulations useful in additive manufacturing such asthree-dimensional inkjet printing, and to methods of additivemanufacturing utilizing same.

Additive manufacturing (AM) is a technology enabling fabrication ofarbitrarily shaped structures directly from computer data via additiveformation steps (additive manufacturing; AM). The basic operation of anyAM system consists of slicing a three-dimensional computer model intothin cross sections, translating the result into two-dimensionalposition data and feeding the data to control equipment which fabricatesa three-dimensional structure in a layerwise manner.

Additive manufacturing entails many different approaches to the methodof fabrication, including three-dimensional printing such as 3D inkjetprinting, electron beam melting, stereolithography, selective lasersintering, laminated object manufacturing, fused deposition modeling andothers.

Three-dimensional (3D) printing processes, for example, 3D inkjetprinting, are being performed by a layer by layer inkjet deposition ofbuilding materials. Thus, a building material is dispensed from adispensing head having a set of nozzles to deposit layers on asupporting structure. Depending on the building material, the layers maythen be cured or solidified using a suitable technique.

Various three-dimensional printing techniques exist and are disclosedin, e.g., U.S. Pat. Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334,6,863,859, 7,183,335, 7,209,797, 7,225,045, 7,300,619, and 7,500,846 andU.S. patent application having Publication No. 20130073068, all by thesame Assignee.

During the additive manufacturing (AM) process, the building materialmay include “model material” (also known as “object material” or“modeling material”), which is deposited to produce the desired object,and frequently, another material (“support material” or “supportingmaterial”) is used to provide temporary support to the object as it isbeing built. The other material is referred to herein and in the art as“support material” or “supporting material”, and is used to supportspecific areas of the object during building and for assuring adequatevertical placement of subsequent object layers. For example, in caseswhere objects include overhanging features or shapes, e.g. curvedgeometries, negative angles, voids, and the like, objects are typicallyconstructed using adjacent support constructions, which are used duringthe printing and then subsequently removed in order to reveal the finalshape of the fabricated object.

Formulations for providing the model material and the support material,referred to as building material formulations or simply as buildingformulations, may be initially liquid and subsequently hardened to formthe required layer shape. The hardening process may be performed by avariety of techniques, such as UV curing, phase change, crystallization,drying, etc. In all cases, the support material is deposited inproximity of the model material, enabling the formation of complexobject geometries and filling of object voids. In such cases, theremoval of the hardened support material is liable to be difficult andtime consuming, and may damage the formed object.

When using currently available commercial print heads, such as ink-jetprinting heads, the building material formulations (the modelformulation and support formulation) should have a relatively lowviscosity (about 10-20 cPs) at the working, i.e., jetting, temperature,such that it can be jetted. Further, the model and support materialformulations should harden (e.g., cure) rapidly in order to allowbuilding of subsequent layers. Additionally, the hardened supportmaterial should have sufficient mechanical strength for holding themodel material in place, and low distortion for avoiding geometricaldefects.

Known methods for removal of support materials include mechanicalimpact, which is typically applied by a tool or water-jet, as well aschemical methods, such as dissolution in a solvent, with or withoutheating. The mechanical methods are labor, intensive and are oftenunsuited for small intricate parts.

For dissolving the support materials, the fabricated object is oftenimmersed in water or in a solvent that is capable of dissolving thesupport materials. The solutions utilized for dissolving the supportmaterial are also referred to herein and in the art as “cleaningsolutions”. In many cases, however, the support removal process mayinvolve hazardous materials, manual labor and/or special equipmentrequiring trained personnel, protective clothing and expensive wastedisposal. In addition, the dissolution process is usually limited bydiffusion kinetics and may require very long periods of time, especiallywhen the support constructions are large and bulky. Furthermore,post-processing may be necessary to remove traces of a ‘mix layer’ onobject surfaces. The term “mix layer” refers to a residual layer ofmixed hardened model and support materials formed at the interfacebetween the two materials on the surfaces of the object beingfabricated, by model and support materials mixing into each other at theinterface between them.

Both mechanical and dissolution methods for removal of support materialsare especially problematic for use in an office environment, whereease-of-use, cleanliness and environmental safety are majorconsiderations.

Water-soluble materials for 3D building have been previously described.U.S. Pat. No. 6,228,923, for example, describes a water solublethermoplastic polymer—Poly(2-ethyl-2-oxazoline)—for use as a supportmaterial in a 3D building process involving high pressure and hightemperature extrusion of ribbons of selected materials onto a plate.

A water-containing support material comprising a fusible crystal hydrateis described in U.S. Pat. No. 7,255,825.

Compositions suitable for support in building a 3D object are described,for example, in U.S. Pat. Nos. 7,479,510, 7,183,335 and 6,569,373, allto the present Assignee. Generally, the compositions disclosed in thesepatents comprise at least one UV curable (reactive) component, e.g., anacrylic component, at least one non-UV curable component, e.g. a polyolor glycol component, and a photoinitiator. After irradiation, thesecompositions provide a semi-solid or gel-like material capable ofdissolving upon exposure to water, to an alkaline or acidic solution orto a water detergent solution. 3D printing methodologies using such asoluble support material are also known as “Soluble Support Technology”or SST, and the support material formulation is often referred to a“soluble support material” or “soluble support material formulation”.Soluble support materials should beneficially feature sufficient watersolubility, so as to be removed during a relatively short time period,or sufficient solubility in a non-hazardous cleaning solution, yet, atthe same, to exhibit mechanical properties sufficient to support theprinted object during the additive manufacturing process.

Additional Background art includes U.S. patent application havingPublication No. 2003/0207959; PCT International Patent Applicationhaving Publication No. WO2015/118552 and PCT International PatentApplication No. IL2016/050886.

SUMMARY OF THE INVENTION

The present inventors have now designed and successfully practiced novelformulations which can be beneficially used in additive manufacturingprocesses, such as 3D inkjet printing. These formulations are designedsuch that the hardened (e.g., cured) material obtained therefrom (uponexposure to curing energy; e.g., light irradiation) is breakable uponimmersion in an aqueous solution (e.g., in water).

The formulations described herein include a combination of amono-functional curable component and a multi-functional curable(reactive) component, and optionally non-curable components, asdescribed herein, selected so as to provide a cured material that breaksinto small particles (physically decomposes) upon immersion in water andcan thus be, for example, readily separated from other components in afabricated object.

According to an aspect of some embodiments of the present inventionthere is provided a curable formulation comprising at least onemono-functional curable material and at least one multi-functionalcurable material, the mono-functional and multi-functional curablematerials being selected such that a cured material formed upon exposingthe formulation to a curing energy is water-breakable.

According to some of any of the embodiments described herein, the atleast one mono-functional curable monomer is represented by Formula I:

wherein:

Ra is hydrogen, alkyl or cycloalkyl; and

Z is represented by X-L-Y,

wherein:

-   -   X is selected from C(═O), C(═O)—NR₁, C(═O)—O, P(═O)—(OR₂)—O or        is absent;    -   Y is selected from O⁻M⁺, OR₃, NR₄R₅ or N⁺R₄R₅R₆Q⁻;    -   L is a hydrocarbon moiety of 1 to 40 atoms in length, optionally        interrupted by one or more heteroatom(s), the heteroatoms being        independently selected from O, S and NR₂, or is absent;    -   Q⁻ is a negatively charged counter ion;    -   M⁺ is a positively charged counter ion;    -   R₁ and R₂ are each independently selected from hydrogen, alkyl        and cycloalkyl;    -   R₃ is selected from hydrogen, alkyl, cycloalkyl and aryl; and    -   R₄, R₅ and R₆ are each independently selected from hydrogen,        alkyl and cycloalkyl, or, alternatively, R₄ and R₅ form a cyclic        ring.

According to some of any of the embodiments described herein, Y isN⁺R₄R₅R₆Q.

According to some of any of the embodiments described herein, L is ahydrocarbon moiety of 1 to 4 carbon atoms in length.

According to some of any of the embodiments described herein, X isselected from C(═O)—NR₁ and C(═O)—O.

According to some of any of the embodiments described herein, Y isNR₄R₅.

According to some of any of the embodiments described herein, L isabsent.

According to some of any of the embodiments described herein, R₄ and R₅form together a cyclic ring, the cyclic ring being a heteroalicyclic.

According to some of any of the embodiments described herein, X isC(═O).

According to some of any of the embodiments described herein, Ra ishydrogen.

According to some of any of the embodiments described herein, Y is OR₃.

According to some of any of the embodiments described herein, L is ahydrocarbon moiety interrupted by one or more heteroatom(s).

According to some of any of the embodiments described herein, Lcomprises alkylene glycol moiety.

According to some of any of the embodiments described herein, X isC(═O).

According to some of any of the embodiments described herein, L is apoly(alkylene glycol) moiety of from 2 to 20 alkylene glycol units.

According to some of any of the embodiments described herein, Ra ishydrogen.

According to some of any of the embodiments described herein, themono-functional curable material is characterized as forming a polymeric(cured) material featuring a water uptake of at least 200%.

According to some of any of the embodiments described herein, themono-functional curable material is characterized as forming a polymeric(cured) material featuring a hydrophilic lipophilic balance, determinedaccording to Davies method, of at least 10.

According to some of any of the embodiments described herein, themono-functional curable material is characterized as forming a polymeric(cured) material featuring a water solubility at least 50 weightpercents.

According to some of any of the embodiments described herein, the atleast one multi-functional curable material is:

-   -   (i) characterized as forming a polymer featuring a Tg higher        than 20° C.; and/or    -   (iii) is represented by Formula II:

wherein:

-   -   Rb is hydrogen, alkyl or cycloalkyl;    -   n is an integer of from 2 to 10, representing a number of        polymerizable groups ═C(Rb)—W—;    -   W in each of the polymerizable groups is independently selected        from C(═O)—O, C(═O)—NR₈, and C(═O) or is absent; and    -   B is a hydrocarbon moiety of 1 to 20 atoms, interrupted and/or        substituted by at least one hydrogen donor-containing group.

According to some of any of the embodiments described herein, themulti-functional curable material is characterized as forming a polymerfeaturing the Tg higher than 20° C., or higher than 30° C., or higherthan 50° C., or higher than 80° C.

According to some of any of the embodiments described herein, themulti-functional curable material is represented by Formula H.

According to some of any of the embodiments described herein, thehydrogen donor-containing group is selected from oxygen, hydroxy,hydroxyalkyl, amine, aminoalkyl, thiol, thioalkyl.

According to some of any of the embodiments described herein, W in eachof the polymerizable groups is independently selected from C(═O)—O,C(═O)—NR₈, and C(═O).

According to some of any of the embodiments described herein, thehydrogen donor-containing group is amine.

According to some of any of the embodiments described herein, B is adiaminoalkylene.

According to some of any of the embodiments described herein, B is1,2-diaminoethylene.

According to some of any of the embodiments described herein, n is 2 andW in each of the polymerizable groups are each C(═O).

According to some of any of the embodiments described herein, thehydrogen donor-containing group is or comprises hydroxy.

According to some of any of the embodiments described herein, B is ahydrocarbon chain substituted by at least one hydroxy.

According to some of any of the embodiments described herein, Bcomprises at least one alkylene glycol moiety.

According to some of any of the embodiments described herein, thehydrogen donor-containing group is hydroxyalkyl.

According to some of any of the embodiments described herein, B is analkylene of 1-4 carbon atoms, substituted by at least one hydroxyalkyl.

According to some of any of the embodiments described herein, B is ahydrocarbon chain interrupted by at least one oxygen atom.

According to some of any of the embodiments described herein, n is atleast 3.

According to some of any of the embodiments described herein, W is eachof the polymerizable groups is C(═O)—O.

According to some of any of the embodiments described herein, aconcentration of the at least one mono-functional curable materialranges from 40 to 90, or from 40 to 80, weight percents of the totalweight of the formulation.

According to some of any of the embodiments described herein, aconcentration of the at least one multi-functional curable material isat least 5 weight percents of the total weight of the formulation.

According to some of any of the embodiments described herein, aconcentration of the multi-functional curable material ranges from 5 to60 weight percents of the total weight of the formulation.

According to some of any of the embodiments described herein, a type andconcentration of each of the multi-functional curable material and themono-functional curable monomer provides a cured material featuring adegree of cross-linking that ranges from about 10% to about 80%, or fromabout 20% to about 70%.

According to some of any of the embodiments described herein, theformulation further comprises at least one non-curable material.

According to some of any of the embodiments described herein, the atleast one non-curable material comprises a water-miscible polymer.

According to some of any of the embodiments described herein, aconcentration of the non-curable material ranges from 1 to 10 weightpercents of the total weight of the formulation.

According to some of any of the embodiments described herein, theformulation further comprises an initiator.

According to some of any of the embodiments described herein, theformulation further comprises an additional agent, such as a surfaceactive agent and/or an inhibitor.

According to some of any of the embodiments described herein, theformulation is curable upon exposure to UV radiation.

According to some of any of the embodiments described herein, theaqueous solution is water.

According to some of any of the embodiments described herein, the curedmaterial breaks upon the immersion into particles having a size rangingfrom 1 micron to 100 mm.

According to some of any of the embodiments described herein, at least50% of the particles have a size lower than 10 mm.

According to some of any of the embodiments described herein, at least50% of the particles have a size lower than 5 mm.

According to some of any of the embodiments described herein, at least50% of the particles have a size lower than 3 mm, or lower than 2.5 mm.

According to some of any of the embodiments described herein, the curedmaterial features a degree of cross linking that ranges from 10 to 80,or from 20 to 70%.

According to some of any of the embodiments described herein, the curedmaterial is characterized by swelling capacity of from 10 to 300, orfrom 10 to 200, or from 10 to 150, or from 20 to 150% by weight.

According to some of any of the embodiments described herein, a 3-gramcube made of the cured material breaks upon static immersion in water inless than 10 hours, or less than 8 hours, or less than 6 hours, or lessthan 4 hours, or less than 3 hours, or less than 2 hours, or less than 1hour.

According to some of any of the embodiments described herein, theformulation is as a building material formulation for additivemanufacturing process.

According to some of any of the embodiments described herein, theprocess is a 3D-inkjet printing.

According to some of any of the embodiments described herein, theformulation is usable as a support material formulation.

According to an aspect of some embodiments of the present inventionthere is provided a method of fabricating a three-dimensional modelobject, the method comprising dispensing a building material so as tosequentially form a plurality of layers in a configured patterncorresponding to the shape of the object, wherein the building materialcomprises the curable formulation according to any one of the respectiveembodiments and any combination thereof.

According to some of any of the embodiments described herein, thebuilding material comprises a modeling material formulation and asupport material formulation, the support material formulationcomprising the curable formulation of any one of claims 1-57.

According to some of any of the embodiments described herein, the methodfurther comprises, subsequent to the dispensing, exposing the buildingmaterial to curing energy, to thereby obtain a printed objected whichcomprises a cured support material formed of the curable formulation.

According to some of any of the embodiments described herein, the methodfurther comprises removing the cured support material, to thereby obtainthe three-dimensional model object.

According to some of any of the embodiments described herein, theremoving comprises contacting the cured support material with water.

According to some of any of the embodiments described herein, thecontacting comprises static immersion of the cured support material inthe water.

According to an aspect of some embodiments of the present inventionthere is provided a three-dimensional object fabricated by the method asdescribed herein in any of the respective embodiments and anycombination thereof.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

Implementation of the method and/or system of embodiments of theinvention can involve performing or completing selected tasks manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of embodiments of the method and/or systemof the invention, several selected tasks could be implemented byhardware, by software or by firmware or by a combination thereof usingan operating system.

For example, hardware for performing selected tasks according toembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to embodiments of theinvention could be implemented as a plurality of software instructionsbeing executed by a computer using any suitable operating system. In anexemplary embodiment of the invention, one or more tasks according toexemplary embodiments of method and/or system as described herein areperformed by a data processor, such as a computing platform forexecuting a plurality of instructions. Optionally, the data processorincludes a volatile memory for storing instructions and/or data and/or anon-volatile storage, for example, a magnetic hard-disk and/or removablemedia, for storing instructions and/or data. Optionally, a networkconnection is provided as well. A display and/or a user input devicesuch as a keyboard or mouse are optionally provided as well.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 presents a schematic illustration of the decomposition of ahighly cross-linked cured material obtained from an exemplary curableformulation according to some embodiments of the present invention, uponinteraction with water.

FIGS. 2A-B present an image of an owl-shaped object, fabricated by a 3Dinkjet process using a curable formulation according to some embodimentsof the present invention as a support material formulation, upon removalof the cured support material in water (FIG. 2A), and a bar graphshowing the time by which a cured support material made from exemplaryformulations according to embodiments of the present invention(breakable type 1 and breakable type 2) from the owl object upon staticimmersion in 3 L water compared to other soluble support materials (type1 support reference and type 2 support reference).

FIGS. 3A-C present a particles size distribution determined as describedin Example 4, of particles obtained upon breakage of a printed curedsample obtained from a curable formulation comprising AG-130G as amono-functional curable material, and, as a multi-functional curablematerial SR368 (FIG. 3A), SR355 (FIG. 3B) and SR399 (FIG. 3C), atvarious degrees of cross-linking.

FIGS. 4A-B present a particles size distribution determined as describedin Example 4, of particles obtained upon breakage of a molded curedsample obtained from a curable formulation comprising AG-130G as amono-functional curable material and SR399 as a multi-functional curablematerial (FIG. 4A), and from a curable formulation comprising DMAPAA-Qas a mono-functional curable material and SR444D as a multi-functionalcurable material (FIG. 4B), at various degrees of cross-linking.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to additivemanufacturing (AM), and more particularly, but not exclusively, towater-breakable formulations useful in additive manufacturing such asthree-dimensional inkjet printing, and to methods of additivemanufacturing utilizing same.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

In a search for formulations suitable for use in additive manufacturing,for example, 3D inkjet printing, the present inventors have designed andsuccessfully practiced novel formulations which are breakable uponimmersion in water within exceptionally short time periods, ranging fromminutes to several (e.g., 2-3) hours.

As discussed hereinabove, soluble formulations commonly used in additivemanufacturing processes such as 3D inkjet printing are designed tofeature high water solubility, and high swelling capacity (waterabsorbance). Such formulations typically comprise hydrophilic curablematerials that upon curing form a cured material that often acts as asuperabsorbent, namely, it is characterized by high swelling capacitydue to the capability of the cured material to form hydrogen bonds withwater molecules. Superabsorbents are typically characterized by a lowcross-linking degree (low cross-linking density) and a swelling capacityas high as 400% or even 500%.

The present inventors have envisioned that a curable formulation whichcan form a cured material that is breakable upon contacting an aqueoussolution can be beneficially used in additive manufacturing processes.In a search for such formulations, the present inventors have uncoveredthat such a water-breakable cured material can be formed while using amixture of mono-functional and multi-functional curable materials whichfeature a combination of properties, such as one or more of rigidity,charge, water absorbance, and hydrophilicity/lipophilicity ratio andother properties, as discussed hereinunder, and which together provide acured material that exhibits properties which render it water-breakable,such as, but not limited to, one or more of degree of crosslinking,rigidity, water absorbance and/or other properties, as discussedhereinunder. As demonstrated in the Examples section that follows,selected combinations that feature such properties were indeed shown toform, upon curing, a cured material that when immersed in water, absorbsthe water up to a point where it breaks into pieces (physicallydecomposes).

By “breakable” or “breakability” it is meant herein a capability of apolymeric material to physically decompose (as opposed, for example, tochemical degradation or dissolution). In some embodiments, a breakablematerial decomposes, or breaks, into pieces, as described herein.

By “water breakable” it is meant herein a capability of a polymericmaterial to break, as defined herein, upon immersion in water and/orupon immersion in an aqueous solution other than water (for example,non-distilled water or other salt-containing aqueous solutions). In someembodiments, a water-breakable material breaks upon static immersion inwater. The material breaks spontaneously, namely, without applying anyphysical or mechanical force other than contacting an aqueous solutionsuch as water.

Reference is now made to FIG. 1, which schematically describes anexemplary cured material according to the rationale underlying thepresent invention. As shown therein a cured material features apolymeric network which comprises a plurality of polymeric chains (blackcurved lines), and chemical cross-linking (red curved lines) as well asother intermolecular interactions, such as, for example, hydrogen bonds(blue dashed lines), between the polymeric chains.

Without being bound by any particular theory, it is assumed that uponcontacting water, water molecules enter between the polymeric chains,and interfere with the hydrogen bonds formed between the chains andoptionally with other intermolecular interactions. However, and furtherwithout being bound by any particular theory, due to the waterabsorbance capability of at least some of the curable materials formingthe polymerized material and a certain degree of covalent cross-linking,and/or the relatively rigid nature of the polymerized material accordingto embodiments of the present invention, the diffusion of watermolecules into the polymeric network apply pressure to the polymericnetwork and as a result, the polymerized (cured) material spontaneouslybreaks into particles.

The curable formulations described herein are therefore designed capableof forming a water-breakable cured material. Such formulations areparticularly usable as support material formulations in additivemanufacturing processes such as 3D inkjet printing, which can be easilyremoved upon immersion in water, without subjecting a fabricated objectto mechanical and/or chemical means which can adversely affect theobject and/or are laborious or environmentally unfriendly. Suchformulations, however, are also usable as modeling materialformulations, for example, for fabricating water-breakable objects.

As shown in FIGS. 2A-B, the novel formulations described herein weresuccessfully utilized for forming a cured support material in 3D inkjetprinting methods, which is completely removed within exceptionally shorttime periods, upon simple immersion in water, and thus supersedescurrently known and/or available formulations for forming solublehardened support materials.

As shown in FIGS. 3A-C and 4A-B, exemplary novel formulations accordingto some embodiments of the present invention form a cured material whichbreaks, upon immersion in water, to thereby form a plurality ofparticles with an average particles size (e.g., a particles size of 50%of the particles) of up to about 4 mm.

Herein throughout, the term “object” or “printed object” or “fabricatedobject” describes a product of an additive manufacturing process. Thisterm refers to the product obtained by a method as described herein,before removal of the cured support material. A printed object istherefore made of hardened (e.g., cured) modeling material and hardened(e.g., cured) support material, or, collectively, of a hardened buildingmaterial.

The term “printed object” as used herein throughout refers to a wholeprinted object or a part thereof.

The term “model”, as used herein, describes a final product of themanufacturing process. This term refers to the product obtained by amethod as described herein, after removal of the support material. Themodel therefore essentially consists of a cured modeling material,unless otherwise indicated. This term is also referred to herein as“model object”, “final object” or simply as “object”.

The terms “model”, “model object”, “final object” and “object”, as usedherein throughout, refer to a whole object or a part thereof.

Herein throughout, the phrase “uncured building material” collectivelydescribes the materials that are dispensed during the fabricationprocess so as to sequentially form the layers, as described herein. Thisphrase encompasses uncured materials dispensed so as to form the printedobject, namely, one or more uncured modeling material formulation(s),and optionally uncured materials dispensed so as to form the support,namely uncured support material formulations.

Herein throughout, the phrase “modeling material formulation”, which isalso referred to herein interchangeably as “modeling formulation” orsimply as “formulation”, describes a part of the uncured buildingmaterial which is dispensed so as to form the model object, as describedherein. The modeling formulation is an uncured modeling formulation,which, upon exposure to curing energy, forms the final object or a partthereof.

An uncured building material can comprise one or more modelingformulations, and can be dispensed such that different parts of themodel object are made upon curing different modeling formulations, andhence are made of different cured modeling materials or differentmixtures of cured modeling materials.

Herein throughout, the phrase “support material formulation”, which isalso referred to herein interchangeably as “support formulation”,describes a part of the uncured building material which is dispensed soas to form the support material, as described herein. The supportmaterial formulation is an uncured formulation, which, upon exposure tocuring energy, forms the hardened support material.

Herein throughout, the phrases “cured modeling material” and “hardenedmodeling material”, which are used interchangeably, describe the part ofthe building material that forms a model object, as defined herein, uponexposing the dispensed building material to curing, and followingremoval of the cured support material, if present. The cured modelingmaterial can be a single cured material or a mixture of two or morecured materials, depending on the modeling material formulations used inthe method, as described herein.

Herein throughout, the phrase “hardened support material” is alsoreferred to herein interchangeably as “cured support material” or simplyas “support material” and describes the part of the hardened (cured)building material that is intended to support the fabricated finalobject during the fabrication process, and which is removed once theprocess is completed and a hardened modeling material is obtained.

In some of any of the embodiments described herein, an uncuredformulation (of a building material, a support material and a modelingmaterial) is typically a curable formulation, which forms a hardenedmaterial upon curing.

Herein throughout, the term “curable formulation” describes a mixture ofmaterials which, when exposed to curing energy, as described herein,solidifies or hardens to form a cured material as defined herein.Curable formulations comprise one or more curable materials, and mayoptionally further comprise one or more non-curable materials,initiators, and other additives.

The term “curable material” describes a compound or a mixture ofcompounds which are typically polymerizable materials that undergopolymerization and/or cross-linking, and thus cure or harden, whenexposed to a suitable curing energy.

Curable materials can be monomeric and/or oligomeric and/or polymericcompounds.

A “curable material” is also referred to herein and in the art as“reactive” material.

The polymerization and/or cross-linking of curable materials can beeffected via any known polymerization reaction, for example, free radialpolymerization, cationic polymerization, and the like.

In some of any of the embodiments described herein, a curable materialis a photopolymerizable material, which polymerizes or undergoescross-linking upon exposure to radiation, as described herein, and insome embodiments the curable material is a UV-curable material, whichpolymerizes and/or undergoes cross-linking upon exposure to UV-visradiation, as described herein.

In some embodiments, a curable material as described herein is apolymerizable material that polymerizes via photo-induced radicalpolymerization.

Alternatively, a curable material is a thermo-curable material whichpolymerizes and/or undergoes cross-linking when exposed to thermalcuring (exposed to heat energy).

In some of any of the embodiments described herein, a curable materialcan comprise a monomer, and/or an oligomer and/or a short-chain polymer,each being polymerizable and/or cross-linkable as described herein.

In some of any of the embodiments described herein, when a curablematerial is exposed to curing energy (e.g., radiation), it polymerizesby any one, or combination, of chain elongation and cross-linking.

In some of any of the embodiments described herein, a curable materialis a monomer or a mixture of monomers which can form a polymericmaterial upon a polymerization reaction, when exposed to curing energyat which the polymerization reaction occurs. Such curable materials arealso referred to herein as “monomeric curable materials”, or as “curablemonomers”.

In some of any of the embodiments described herein, a curable materialis a polymer or an oligomer or a mixture of polymers and/or oligomerswhich can form a polymeric material upon a polymerization and/orcross-linking reaction, when exposed to curing energy at which thepolymerization and/or cross-linking reaction occurs.

A curable material can comprise a mono-functional curable materialand/or a multi-functional curable material.

Herein, a mono-functional curable material comprises one functionalgroup that can undergo polymerization when exposed to curing energy(e.g., radiation). A multi-functional curable material comprises two ormore groups that can undergo polymerization when exposed to curingenergy (e.g., radiation), and which in addition can participate inchemical cross-linking of polymeric chains formed upon exposure tocuring energy.

When curable materials are polymerizable and/or cross-linkablematerials, the cured material formed upon exposure to curing energy is apolymerized material or a polymeric network (e.g., a plurality ofpolymeric chains, at least two being cross-linked to one another), asdescribed herein.

Herein, the phrases “exposing to a curing energy”, “exposing to curing”,“exposing to curing conditions” and “exposing to an energy source thataffects curing”, and grammatically diversions thereof, are usedinterchangeably, and mean that dispensed layers of uncured buildingmaterial are exposed to the curing energy and the exposure is typicallyperformed by applying a curing energy to the dispensed layers.

A “curing energy” typically includes application of radiation orapplication of heat.

The radiation can be electromagnetic radiation (e.g., ultraviolet orvisible light), or electron beam radiation, or ultrasound radiation ormicrowave radiation, depending on the materials to be cured. Theapplication of radiation (or irradiation) is effected by a suitableradiation source. For example, an ultraviolet or visible or infrared orXenon lamp can be employed, as described herein.

A curable material or system that undergoes curing upon exposure toradiation is referred to herein interchangeably as “photopolymerizable”or “photoactivatable” or “photocurable”.

When the radiation is a UV radiation, the curable material is referredto herein as UV-curable.

When the curing energy comprises heat, the curing is also referred toherein and in the art as “thermal curing” and comprises application ofthermal energy. Applying thermal energy can be effected, for example, byheating a receiving medium onto which the layers are dispensed or achamber hosting the receiving medium, as described herein. In someembodiments, the heating is effected using a resistive heater.

In some embodiments, the heating is effected by irradiating thedispensed layers by heat-inducing radiation. Such irradiation can beeffected, for example, by means of an IR lamp or Xenon lamp, operated toemit radiation onto the deposited layer.

A curable material or system that undergoes curing upon exposure to heatis referred to herein as “thermally-curable” or “thermally-activatable”or “thermally-polymerizable”.

Herein throughout, the phrase “cleaning time” describes the time neededto remove a cured support material from a fabricated object.

According to some embodiments of the present invention, the “cleaningtime” equals to the time required for an amount of a cured material asdescribed herein to break into small pieces upon immersion in water.This time can be measured by recording the time from immersing a curedmaterial is water to when the cured material no longer decomposes, forexample, the time at which no more change in the size of material'sparticles is observed.

Herein throughout, whenever the phrase “weight percents” is indicated inthe context of embodiments of a curable formulation, it is meant weightpercents of the total weight of the formulation as described herein.

The phrase “weight percents” is also referred to herein as “% by weight”or “% wt.” or “wt. %”.

Herein throughout, some embodiments of the present invention aredescribed in the context of the additive manufacturing being a 3D inkjetprinting. However, other additive manufacturing processes, such as, butnot limited to, SLA and DLP, are contemplated.

The Curable Formulations:

The present inventors have designed and successfully prepared andpracticed curable formulations which provide a cured material that ischaracterized as a water breakable material, as defined herein.

A breakability of a cured (polymerized) material, according to someembodiments of the present invention, can be effected upon uptake(swelling, absorbance) of water (or any other aqueous solution) in anamount which is from about 1% to about 300% the material's weight, orfrom 5% to 300%, or from 10% to 300%, or from 10% to 150%, or from 20%to 150%, including any subranges and intermediate values therebetween.

In some embodiments, a cured material as described herein is capable ofswelling (absorbing) water (or any other aqueous solution) in an amountwhich is no more than 500% of its weight before is breaks into pieces.In some embodiments, a cured material as described herein is capable of(absorbing) water (or any other aqueous solution) in an amount which isno more than 400%, or no more than 350%, or no more than 300%, or nomore than 250%, or no more than 200%, or no more than 150%, or no morethan 120%, or no more than 100%, or no more than 95%, or no more than90%, or no more than 85%, or no more than 80%, or no more than 75%, orno more than 70%, or no more than 65%, or no more than 60%, or no morethan 55%, or no more than 50%, or no more than 45%, or no more than 40%,or no more than 35%, or no more than 30%, or no more than 25%, or nomore than 20%, or no more than 15%, or no more than 10%, or no more than5%, of its weight, before is breaks into pieces (physically decomposes).

In some of these embodiments, a cured material as described herein iscapable of swelling (absorbance) water (or an aqueous solution) at aweight which is at least 0.1%, or at least 0.5%, or at least 1%, or atleast 5%, or at least 8%, or at least 10%, of its weight before isbreaks into pieces.

In some embodiments, a cured material as described herein is capable ofswelling (absorbing) water (or any other aqueous solution) in an amountwhich is from about 1% to about 300% the material's weight, or from 5%to 300%, or from 10% to 300%, or from 10% to 150%, including anysubranges and intermediate values therebetween, of its weight, before itbreaks into pieces (physically decomposes). According to some of any ofthe embodiments described herein, the water breakable material breaks(physically decomposes), upon immersion in water, into particles whichcan be, for example, from 50% to 0.001% in size, of the size of thecured material.

Herein throughout, the term “particles” describes small pieces of thewater-breakable material, which can adopt any shape and any size, forexample, as described herein. The term “particles” is also referred toherein interchangeably as “grains”, “pieces” and any other art synonym.

According to some of any of the embodiments described herein, the waterbreakable material breaks (physically decomposes), upon immersion inwater, into particles having an average size of up to 10 mm. Accordingto some of any of the embodiments described herein, the water breakablematerial breaks (physically decomposes), upon immersion in water, intoparticles having an average size of up to 8 mm. According to some of anyof the embodiments described herein, the water breakable material breaks(physically decomposes), upon immersion in water, into particles havingan average size of up to 6 mm. According to some of any of theembodiments described herein, the water breakable material breaks(physically decomposes), upon immersion in water, into particles havingan average size of up to 5 mm. According to some of any of theembodiments described herein, the water breakable material breaks(physically decomposes), upon immersion in water, into particles havingan average size of up to 4 mm. According to some of any of theembodiments described herein, the water breakable material breaks(physically decomposes), upon immersion in water, into particles havingan average size of up to 3 mm. According to some of any of theembodiments described herein, the water breakable material breaks(physically decomposes), upon immersion in water, into particles havingan average size of up to 2 mm.

By “average size” of the particles, it is meant a size which 50% of theparticles do not exceed and 50% of the particles do exceed, and is alsoreferred to in the art as d50.

In some embodiments, the cured material breaks into a plurality ofparticles, at least 50%, or at least 70%, or at least 90% of theparticles having a size in a range of from few microns (e.g., 1, 2, 3, 4or 5 microns) to about 10 mm. In some embodiments, the cured materialbreaks into a plurality of particles, at least 50%, or at least 70%, orat least 90% of the particles having a size in a range of from 1, 2, 3,4 or 5 microns to about 8 mm. In some embodiments, the cured materialbreaks into a plurality of particles, at least 50%, or at least 70%, orat least 90% of the particles having a size in a range of from 1, 2, 3,4 or 5 microns to about 8 mm. In some embodiments, the cured materialbreaks into a plurality of particles, at least 50%, or at least 70%, orat least 90% of the particles having a size in a range of from 1, 2, 3,4 or 5 microns to about 6 mm. In some embodiments, the cured materialbreaks into a plurality of particles, at least 50%, or at least 70%, orat least 90% of the particles having a size in a range of from 1, 2, 3,4 or 5 microns to about 5 mm. In some embodiments, the cured materialbreaks into a plurality of particles, at least 50%, or at least 70%, orat least 90% of the particles having a size in a range of from 1, 2, 3,4 or 5 microns to about 4 mm. In some embodiments, the cured materialbreaks into a plurality of particles, at least 50%, or at least 70%, orat least 90% of the particles having a size in a range of from 1, 2, 3,4 or 5 microns to about 3 mm. In some embodiments, the cured materialbreaks into a plurality of particles, at least 50%, or at least 70%, orat least 90% of the particles having a size in a range of from 1, 2, 3,4 or 5 microns to about 2 mm. In some embodiments, the cured materialbreaks into a plurality of particles, at least 50%, or at least 70%, orat least 90% of the particles having a size in a range of from 100microns to about 8 mm, or from about 100 microns to about mm, or fromabout 100 microns to about 5 mm, or from about 100 microns to about 4mm. Intermediate values and subranges within any of the foregoing rangesare contemplated herewith. In some embodiments, the cured materialbreaks into a plurality of particles, at least 50 of the particleshaving a size in a range of from 100 microns to about 4 mm, or to about2 mm. In some embodiments, the cured material breaks into a plurality ofparticles, at least 70 of the particles having a size in a range of from100 microns to about 4 mm, or to about 2 mm. Exemplary particles sizedistribution of cured materials formed of the curable formulationsdescribed herein are presented in FIGS. 3A-C and 4A-B.

According to some embodiments, the curable formulations described hereinare capable of forming a cured material which is such that a 3-gram cubemade of the cured material is breakable, as described herein, uponstatic immersion in water in less than 10 hours, or less than 8 hours,or less than 6 hours, or less than 4 hours, or less than 3 hours, orless than 2 hours, or less than 1 hour, and even less than 40 minutes,less than 30 minutes, less than 20 minutes or less than 10 minutes.

In some of any of the embodiments described herein, a cured materialbreaks upon immersion is water regardless of the ratio between the sizeand/or shape of the cured material and the amount of water it contacts.For example, a 3-gram cube made of the cured material is breakablewithin substantially the same time period when immersed in 50 ml, 100ml, 200 ml, 500, ml, 1 Liter or 1.5 Liter of water. In some embodiments,the time of static immersion of the cured material in water until itbreaks depends on the chemical composition of the cured materials andassociated properties and not on the volume or chemical composition ofthe aqueous formulation in which it is immersed.

According to some embodiments of the present invention, the formulationsdescribed herein are characterized as forming a cured material whichexhibits a relatively low swelling capacity.

Herein throughout, and in the art, the term “swelling capacity”,describes a property of a material to absorb and retain water or anyother aqueous solution, is also referred to herein as “absorbancecapacity” with respect to water to any other aqueous solution, andrefers to the maximal amount of water (or an aqueous solution) that canbe absorbed by the material relative to its weight. This term isexpressed in wt % relative to the material's weight. For example, when100 grams of a material can absorb up to 500 grams water, the wateruptake of the material is considered as 500%; and when 100 grams of amaterial can absorb up 20 grams water, the water uptake of the materialis considered as 20%.

According to some embodiments of the present invention, the formulationsdescribed herein are characterized as forming a cured material whichexhibits a swelling capacity, as defined herein, which is lower than500%, lower than 400%, lower than 350%, lower than 300%, preferablylower than 280%, lower than 250%, lower than 220%, lower than 200%,lower than 180%, lower than 170%, lower than 160%, lower than 150%,lower than 140%, lower than 130%, lower than 120%, lower than 1610%,lower than 100%, and more preferably lower, for example, lower than 90%,lower than 80%, lower than 70%, lower than 60%, lower than 50%, lowerthan 40%, lower than 35%, lower than 30%, lower than 25%, lower than20%, lower than 15%, or as low as 10%.

According to some embodiments of the present invention, the formulationsdescribed herein are characterized as forming a cured material whichexhibits a swelling capacity, as defined herein, that ranges from about10% to about 300% or from about 10% to about 200% or from about 10% toabout 150%, including any intermediate values and subrangestherebetween. It is assumed that higher swelling capacities do notprovide a cured material that is water-breakable as described herein, orwhich does not break into a plurality of particles, as described herein;and that lower swelling capacities do not feature water breakability.

The formulations described herein are alternatively, or in addition,characterized as forming a cured material which exhibits a relativelyhigh degree of covalent cross-linking, as defined herein.

Herein throughout, and in the art, the term “cross-linking” describesthe intermolecular interactions between polymeric chains in apolymerized material (a polymeric network). Such intermolecularinteractions include, for example, hydrogen bonds, electrostaticinteractions, aromatic interactions, and/or covalent cross-linking.

By “covalent cross-linking” or “covalently cross-linked” it is meantthat at least some of the polymeric chains in a polymerized (cured)material are linked to one another via covalent bonds.

The term “cross-linking degree”, which is also referred to herein as“degree of cross-linking” or “DOC”, as used herein, describes acalculated, theoretical value presenting the percentages of the bonds ina polymeric network (e.g., of a cured material as described herein)which are covalent bonds between polymeric chains out of the total bondsformed. This value is calculated based on the amount of amulti-functional curable material relative to the sum of themono-functional curable material and the multifunctional curablematerial in a curable formulation and on the respective percentage ofpolymerizable moieties in a multi-functional curable material out of thetotal number of polymerizable moieties in the formulation, assuming 100%conversion.

In some embodiments, a degree of cross-linking is calculated per thefollowing equation:

DOC=(n _(XL) ×XL _(f))/([(n _(XL) ×XL _(f))+(n _(mm))]

With n_(XL)=Number of moles of a multifunctional curable material;XL_(f)=Number of curable (polymerizable) groups of the multifunctionalcurable material; n_(mm)=Number of mono-functional curable material.

According to some of any of the embodiments described herein, the curedmaterial is characterized by a cross-linking degree, as defined herein,which is at least 1%, or at least 2%, or at least 3%, or at least 4%, orat least 5%, or at least 10%, or at least 15%, or at least 20%, or atleast 25%, or at least 30%, or at least 35%, or at least 40%, or atleast 45%, or at least 50%, or at least 55%, or at least 60%, or atleast 60%, or at least 65%, or at least 70%. According to some of any ofthe embodiments described herein, the cured material is characterized bya cross-linking degree, as defined herein, which ranges from about 1% toabout 90%, or from about 1% to about 80%, or from about 1% to about 70%,or from about 1% to about 60%, or from about 1%, to about 50%, or fromabout 1% to about 40%, or from about 5% to about 80%, or from about 5%to about 65%, preferably from about 10% to about 80%, or from about 10%to about 70%, or from about 10% to about 60%, or from about 20% to about80%, or from about 20% to about 70%, or from about 20% to about 50%,including any intermediate values and subranges therebetween.

By selecting a multi-functional curable material, a mono-functionalcurable material and concentrations of the multi-functional andmono-functional curable materials (e.g., a molar ratio therebetween), adegree of cross-linking of the cured material can be determined.

In some embodiments, and as demonstrated in the Examples section thatfollows, a degree of cross linking affects the particles sizedistribution of the particles obtained upon water-breakage of the curedmaterial.

In some embodiments, the properties of the water breakable curedmaterial, such as the particles size distribution of the particlesobtained upon breakage, is manipulated by selecting a degree of crosslinking of the cured material, that is, by selecting a multi-functionalcurable material, a mono-functional curable material and concentrationsof the multi-functional and mono-functional curable materials (e.g., amolar ratio therebetween), according to the above equation.

The formulations described herein are alternatively, or in addition,characterized as forming a cured material which exhibits a relativelyhigh rigidity (e.g., a relatively high Tg).

According to an aspect of some embodiments of the present invention,there is provided a curable formulation which comprises at least onemono-functional curable material and at least one multi-functionalcurable material, selected so as to provide, upon exposure to a suitablecuring energy, a water-breakable cured material as described herein.

According to some of any of the embodiments described herein, the atleast one mono-functional curable material and the at least onemulti-functional curable material are selected so as to provide, uponexposure to a suitable curing energy, a cured material that features oneor more of the properties described hereinabove.

The Mono-Functional Curable Material:

According to some of any of the embodiments described herein, thecurable formulation comprises one or more mono-functional curablematerial(s), at least one of the mono-functional materials beingrepresented by Formula I:

wherein:

Ra is hydrogen, alkyl or cycloalkyl; and

Z is represented by X-L-Y,

-   -   wherein:    -   X is selected from —C(═O)—, —C(═O)—NR₁—, —C(═O)—O—,        —P(═O)—(OR₂)—O— or is absent;    -   Y is selected from O⁻M⁺, OR₃, NR₄R₅ or N⁺R₄R₅R₆Q⁻;    -   L is a hydrocarbon moiety of 1 to 40 atoms in length, optionally        interrupted by one or more heteroatom(s), the heteroatoms being        independently selected from O, S and NR₂, or is absent;    -   Q is a negatively charged counter ion;    -   M is a positively charged counter ion; and    -   R₁ and R₂ are each independently selected from hydrogen, alkyl        and cycloalkyl;    -   R₃ is selected from hydrogen, alkyl, cycloalkyl and aryl; and    -   R₄, R₅ and R₆ are each independently selected from hydrogen,        alkyl and cycloalkyl, or, alternatively, R₄ and R₅ form a cyclic        ring.

According to some of any of the embodiments described herein for amono-functional curable material represented by Formula i, themono-functional curable material is ionic, namely, it comprises a cationand an anion.

In some of these embodiments, Y is a charged group, which can either bepositively charged group or a negatively charged group, and the curablecompound further comprises a respective counter anion, which ispresented in Formula I as forming a part of Y.

In some of any of the embodiments described herein, when themono-functional curable material is ionic, the formulation may comprisean aqueous solution of the ionic material.

In some of any of the embodiments described herein, the curable materialis ionized when in an aqueous solution.

Exemplary such curable materials are those in which Y is O⁻M⁺, and M⁺ isH⁺.

According to these embodiments, Y is OH and the curable material has apKa lower than 7, such that at a pH above this pKa (e.g., pH 7) thecurable material is ionized.

Exemplary curable material in which Y is OH that is ionized into O⁻M⁺(e.g., at pH 7) include polymerizable carboxylic acids such as, forexample, acrylic acid and vinyl phosphonic acid.

In exemplary embodiments, a mono-functional curable material is acrylicacid, such that in Formula I, X is C(═O), L is absent, Y is O⁻M⁺, and M⁺is H⁺. In some of these embodiments, Ra is H.

In exemplary embodiments, a mono-functional curable material is vinylphosphonic acid, such that in Formula I, X is P(═O)(OR₁), L is absent, Yis O⁻M⁺, and M⁺ is H⁺. In some of these embodiments, Ra is H.

According to some of any of the embodiments described herein for amono-functional curable material represented by Formula I, themono-functional curable material is ionic, and Y is a negatively chargedgroup such as O⁻, and further comprises a M⁺ positively charged counterion (a cation). M⁺ can be H⁺ or can otherwise be a metal cation,preferably a univalent metal cation such as an alkali metal cation(e.g., Na⁺ or K⁺).

According to some of any of the embodiments described herein for amono-functional curable material represented by Formula I, themono-functional curable material is ionic, and Y is a positively chargedgroup such as N⁺R₄R₅R₆, and further comprises a Q⁻ negatively chargedcounter ion (an anion).

The anion Q⁻ can be any univalent anion such as, but not limited to,halide (e.g., chloride, bromide or iodide, preferably chloride),sulfonate (e.g., tosylate, mesylate), oxalate, maleate, and the like.

In some of these embodiments, L is a hydrocarbon moiety, and in someembodiments, the hydrocarbon moiety is of 1 to 8, or 1 to 6, or 1 to 4carbon atoms in length. In some embodiments, L is a hydrocarbon atom of2 or 3 carbon atoms in length.

In some of these embodiments, the hydrocarbon moiety is an alkylene, andin some embodiments, it is an unsubstituted alkylene. The alkylene andcan be, for example, butylenes, propylene ethylene or methylene, and ispreferably ethylene or propylene.

In some of any of the embodiments described herein for Y beingN⁺R₄R₅R₆Q⁻, one or more of R₄-R₆ is other than hydrogen, such that Ycomprises secondary ammonium, or, preferably, a tertiary ammonium or aquaternary ammonium.

In some of these embodiments, each of R₄-R₆ is other than hydrogen.

In some embodiments, two or more, or each of R₄-R₆ is alkyl, as definedherein.

In some of any of the embodiments described herein for the curablemono-functional material being ionic, X is C(═O)—O, such that thecurable material is a mono-functional acrylate, or mono-acrylate. Insome of these embodiments, Ra is hydrogen. In some of these embodiments,Ra is methyl and the curable material is a mono-functional methacrylate.

In some of any of the embodiments described herein for the curablemono-functional material being ionic, X is C(═O)—NR₁, such that thecurable material is a mono-functional acrylamide. In some of theseembodiments, Ra is hydrogen. In some of these embodiments, Ra is methyland the curable material is a mono-functional methacrylamide. In some ofthese embodiments, R₁ is hydrogen.

Curable formulations which comprise a mono-functional curable materialwhich is ionic are also referred to herein as “type 1” formulations.

According to some of any of the embodiments described herein for amono-functional curable material represented by Formula I, themono-functional curable material is non-ionic.

Curable formulations which comprise a mono-functional curable materialwhich is ionic are also referred to herein as “type 2” formulations.

In some of any of the embodiments described herein for a non-ionicmono-functional curable material of Formula I, Y is an amine, forexample NR₄R₅, as presented herein.

In some of these embodiments, the amine is a tertiary amine, such thatR₄ and R₅ are each other than hydrogen.

In some of the embodiments when Y is amine, L is absent, and in some ofthese embodiments, X is C(═O), and the curable material is anacrylamide.

An exemplary heteroalicyclic moiety is morpholine. An exemplary suchcurable material is acryloyl morpholine (ACMO™).

In some of these embodiments, R₄ and R₅ are both alkyl. An exemplarysuch curable material is N,N-diethyl acrylamide (DEAA™).

In some embodiments, L is a hydrocarbon moiety, as described herein, andin some embodiments it is an alkylene, as defined herein, preferably of1 to 4 carbon atoms in length.

In some of these embodiments, Y is amine and R₄ and R₅ are both alkyl.An exemplary such curable material is N,N-dimethylamino propylacrylamide(DMAPAA™).

In some of these embodiments, X is C(═O)—NR₁ and the mono-functionalcurable material is a mono-functional acrylamide, or mono-acrylamide. Insome of these embodiments, Ra is hydrogen. In some embodiments, Ra ismethyl and the mono-functional curable material is a mono-functionalmethacrylamide. In some of these embodiments, R₁ is hydrogen.

In some of these embodiments, X is C(═O)—O and the mono-functionalcurable material is a mono-functional acrylate, or mono-acrylate. Insome of these embodiments, Ra is hydrogen. In some embodiments, Ra ismethyl and the mono-functional curable material is a mono-functionalmethacrylate.

In some embodiments, when Y is amine, as described herein, Ra ishydrogen.

In some of any of the embodiments described herein for a non-ionicmono-functional curable material of Formula I, Y is an alkoxy,represented in Formula I as OR₃, wherein R₃ is other than hydrogen ispreferably an alkyl, as defined herein, and in some embodiments, Y ishydroxy.

In some of any of the embodiments described herein for Y being hydroxyor an alkoxy, L is a hydrocarbon moiety, as defined herein.

In some of these embodiments, L is a hydrocarbon moiety interrupted byone or more heteroatom(s).

In some embodiments, L is or comprises one or more alkylene glycolmoieties.

In some embodiments, L is or comprises an alkylene glycol chain or apoly(alkylene glycol) chain, for example a poly(ethylene glycol) chain,composed of from 2 to 20, or from 2 to 15, or from 5-15 alkylene glycolunits, as defined herein.

In some of any of the embodiments described herein for a Y being alkoxy,X is C(═O)—O, such that the mono-functional curable material is amono-functional acrylate, or monoacrylate. In some embodiments, Ra ishydrogen. Alternatively, Ra is methyl and the curable material is amono-functional or mono-methacrylate.

Exemplary mono-functional acrylates or methacrylates in which Y isalkoxy are mono-functional methyl-PEG (or MPEG) acrylates.

In some of any of the embodiments described herein for a mono-functionalcurable material of Formula I, Ra is hydrogen. In some embodiments, Rais methyl.

It is to be noted that any other compounds encompassed by Formula I asdescribed herein are contemplated as mono-functional curable materialssuitable for inclusion in the curable formulations.

It is to be further noted that it is assumed, without being bound by anyparticular theory, that a curable mono-functional material suitable forinclusion in the curable formulation of the present embodiments shouldbe either ionic and/or feature alkylated functional groups such astertiary amine, tertiary or quaternary ammonium and/or alkoxy.

Exemplary mono-functional material suitable for use in the context ofsome embodiments of the present invention are presented on Table 1hereinbelow.

In some of any of the embodiments described herein, the mono-functionalcurable material formed, upon curing (when used as the only curablematerial) a cured (e.g., polymeric) material that features one or moreof the following characteristics:

a water uptake of at least 200%;

a hydrophilic lipophilic balance, determined according to Davies method,of at least 10; and

a water solubility at least 50 weight percents.

In the context of these embodiments, the phrase “water uptake” whichalso means “water absorbance” means the amount of water the polymericmaterial can absorb when immersed in water, relative to its weight(before contacting water).

In the context of these embodiments, the phrase “water solubility”describes the weight % of a polymer that is added to 100 grams waterbefore the solution becomes turbid (non-transparent).

Exemplary mono-functional curable materials suitable for use in thecontext of the present embodiments are presented in Table 1 in theExamples section that follows.

The Multi-Functional Curable Material:

According to some of any of the embodiments described herein, thecurable formulation comprises one or more multi-functional curablematerial(s), at least one of the multi-functional materials being:

-   -   (i) characterized as forming a polymer featuring a Tg higher        than 20° C.; and/or    -   (iii) represented by Formula II:

wherein:

-   -   Rb is hydrogen, alkyl or cycloalkyl;    -   n is an integer of from 2 to 10;    -   W in each of the polymerizable groups represented by ═C(Rb)—W is        independently selected from C(═O)—O, C(═O)—NR₈, and C(═O) or is        absent; and    -   B is a hydrocarbon moiety of 1 to 20 atoms, or 2 to 20 atoms,        interrupted and/or substituted by at least one hydrogen        donor-containing group.

According to some of any of the embodiments described herein, themulti-functional curable material is characterized as forming a polymer(a cured material), when used per se, which features a Tg higher than20° C., or higher than 30° C., or higher than 40° C., or higher than 50°C., or higher than 60° C., or higher than 70° C., or higher than 80° C.,and even higher, for example from 90° C., 100° C., or higher.

According to some of any of the embodiments described herein, themulti-functional curable material is represented by Formula II.

According to some of any of the embodiments described herein, themulti-functional curable material is represented by Formula II and ischaracterized as forming a cured (polymerized) material that features aTg of at least 20° C. or higher.

The multi-functional curable material can be a di-functional curablematerial, when n in formula II is 2, a tri-functional curable material,when n is 3, a tetra-functional or penta-functional or hexa-functionalcurable material, when n is 4, 5, or 6, respectively.

The multi-functional curable material comprises 2 or more polymerizablegroups, represented by ═C(Rb)—W in Formula II.

The moiety B connects the 2 or more polymerizable groups.

In some of any of the embodiments described herein, n is 2, and themoiety B is a bi-radical moiety that links the two polymerizable groups.

In some of any of the embodiments described herein, n is 3, and themoiety B is a tri-radical moiety that links between the threepolymerizable groups. In some of these embodiments, B is or comprises a3-arm (branching) moiety.

In some of any of the embodiments described herein, n is 4, and themoiety B links between the four polymerizable vinyl groups. In some ofthese embodiments, B is or comprises a 4-arm (branching) moiety, and soforth.

According to some of any of the embodiments described herein, themulti-functional curable material features one or more hydrogendonor-containing group(s), as defined herein, and in some of theseembodiments, B comprises one or more hydrogen donor-containing group.

A hydrogen bond donor is a group that includes an electronegative atomto which a hydrogen atom is covalently bonded. The electronegative atompulls electron density away from the hydrogen atom so that it develops apartial positive charge (S+). Thus, the hydrogen atom can interact withan atom having a partial negative charge (5-), for example, an oxygen ina water molecule, through an electrostatic interaction.

A hydrogen donor-containing group, as used herein, describes a groupthat can participate in hydrogen interactions as a hydrogen bond donor.

Exemplary such groups include an electronegative atom (e.g., oxygen),hydroxy, hydroxyalkyl, amine (primary or secondary), aminoalkyl, thiol,and thioalkyl.

In some of any of the embodiments described herein, B comprises one ormore hydroxy groups and/or one or more hydroxyalkyl groups and/or one ormore amine groups.

In some of any of the embodiments described herein, W in each of thepolymerizable groups is independently selected from C(═O)—O, C(═O)—NR₈,and C(═O).

In some of any of the embodiments described herein, in at least one ofthe polymerizable moieties, W is C(═O)—O.

In some of any of the embodiments described herein, in each of thepolymerizable moieties, W is C(═O)—O. Such multi-functional curablematerials are also referred to as multi-acrylates, and can bedi-acrylates, tri-acrylates, and so forth.

In some of any of the embodiments described herein, the hydrogendonor-containing group is or comprises an amine. Preferably, the amineis a primary amine.

In some of these embodiments, B is or comprises an aminoalkyl, and insome embodiments, B is a diaminoalkylene.

In some of these embodiments, n is 2 and B is a 1,ω-aminoalkylene, inwhich the amino groups are attached to the terminal carbon atoms of thealkylene. Examples include 1,2-diaminoethylene, 1,3-siaminopropylene,1,4-diaminobutylene, and so forth.

In exemplary embodiments, B is 1,2-diaminoethylene.

In some of the embodiments in which B is a 1,ω-aminoalkylene, W in eachof the polymerizable groups is C(═O), and the curable material is adiacrylamide. When Rb is methyl, the curable material is adimethacrylamide.

In some of any of the embodiments described herein for amulti-functional curable material represented by Formula II, thehydrogen donor-containing group is or comprises hydroxy.

In some embodiments, B is a hydrocarbon chain, as described herein,substituted by at least one hydroxy or a hydroxyalkyl.

In some of these embodiments, the hydrocarbon chain comprises one ormore alkylene glycol groups, as described herein, and one or more of thealkylene glycol groups is substituted by a hydroxy or a hydroxyalkyl.

In exemplary embodiments, B comprises one or more propylene glycolgroups, and at least one of the propylene glycol moieties is substitutedby a hydroxy or a hydroxyalkyl.

In some of the embodiments in which B comprises one or more alkyleneglycol groups, and one or more of the alkylene glycol groups issubstituted by a hydroxy.

In some of any of the embodiments described herein for amulti-functional curable material represented by Formula II, thehydrogen donor-containing group is a hydroxyalkyl, for example ahydroxymethyl, a hydroxethyl, a hydroxypropyl, and so forth.

In some of any of the embodiments described herein for amulti-functional curable material represented by Formula II, B is analkylene of 1-10 carbon atoms, or 1-18 carbon atoms, or 1-6 carbonatoms, or 1-4 carbon atoms, in length.

In some of any of the embodiments described herein for amulti-functional curable material represented by Formula II, B is analkylene as described herein, substituted by at least one hydroxyalkyl.

In some of any of the embodiments described herein for amulti-functional curable material represented by Formula II, B is orcomprises a branched alkylene, featuring 3 or more arms, at least one ofwhich is or comprises a hydrogen bond donor-containing group asdescribed herein.

In some of these embodiments, B is or comprises a branched alkylenefeaturing 3 or more arms, and one of these arms is or comprises ahydroxyalkyl.

In some of any of the embodiments described herein for amulti-functional curable material represented by Formula II, B is orcomprises a branched hydrocarbon moiety, interrupted by one or moreoxygen atoms (O atoms).

In some of any of the embodiments described herein for amulti-functional curable material represented by Formula II, B is orcomprises a branched hydrocarbon moiety, optionally interrupted by aheteroatom (e.g., O), and optionally substituted by hydroxy or ahydroxyalkyl.

An exemplary branched hydrocarbon moiety is or comprises a[—(CH₂)a]₃-C—(CH₂)m-O—(CH₂)k-C—[(CH₂)b-]₃, in which a, b, m and k areeach independently 0, 1, 2, 3, to 4 and up to 10, preferably 0-4, andmore preferably from 1-4, and each terminal carbon is linked to apolymerizable group or to hydroxy or to hydrogen.

In some of any of the embodiments described herein for B being orcomprising hydroxy, W is each of the polymerizable groups is C(═O)—O, asdescribed herein.

In some of any of the embodiments described herein, Rb in each of thepolymerizable groups can be the same or different. In some embodiments,Rb in each of the polymerizable groups is independently hydrogen ormethyl. In some embodiments, Rb in each of the polymerizable groups ishydrogen. Alternatively, Rb in each of the polymerizable groups ismethyl.

It is to be noted that any other compounds encompassed by Formula II asdescribed herein are contemplated as multi-functional curable materialssuitable for inclusion in the curable formulations.

Exemplary multi-functional curable materials suitable for use in thecontext of the present embodiments are presented in Table 2 in theExamples section that follows.

A Non-Curable Material:

In some of any of the embodiments described herein, a curableformulation as described herein in any one of the respectiveembodiments, and any combination thereof, in addition to the curablematerials, one or more non-curable materials (also referred to herein as“non-reactive”).

The term “non-curable” encompasses materials that are non-polymerizableunder any conditions and/or are non-polymerizable under conditions atwhich curable materials as described herein are polymerizable, and/orare non-polymerizable under any condition used in a fabrication of anobject. Such materials are typically devoid of a polymerizable group,for example, a UV-photopolymerizable group.

In some embodiments, the non-curable material is non-reactive towardsthe curable materials as described herein, that is, it does not reactwith the curable materials and is incapable of interfering with thecuring thereof, under the fabrication conditions, including the curingconditions.

In some of any of the embodiments described herein, a non-curablematerial is a polymeric material.

In some of any of the embodiments described herein, the non-curablematerial is a water-miscible material, for example, a water-misciblepolymeric material.

In some of any of the embodiments described herein the polymericmaterial is water soluble or water dispersible or water misciblepolymeric material, as defined herein.

In some embodiments, the polymeric material comprises a plurality ofhydrophilic groups as defined herein, either within the backbone chainof the polymer or as pendant groups. Exemplary such polymeric materialsare polyols. Some representative examples include, but are not limitedto, Polyol 3165, polypropylene glycol, polyethylene glycol, polyglycerol, ethoxylated forms of these polymers, paraffin oil and thelike, and any combination thereof.

In some of any of the embodiments described herein, the non-curablematerial is a non-polymeric material, and in some embodiments, it is awater-miscible non-polymeric material such as, for example, 1,3-propanediol, 1,2-propane diol, trimethylolpropane, sorbitol, and Boltron P4290.

Any non-curable materials commonly used in additive manufacturingprocesses, preferably water-miscible non-curable materials, and anycombination thereof, are contemplated.

Additional Agents:

A curable formulation as described herein in any of the respectiveembodiments can further comprise additional agents, for example,initiators, inhibitors, stabilizers and the like.

In some of any of the embodiments described herein, and any combinationthereof, the curable formulation further comprises an initiator, forinducing a polymerization of the curable materials upon exposure tocuring energy or curing conditions.

In some of these embodiments, one or more or all of the curablematerials is a UV-curable material and the initiator is aphotoinitiator.

The photoinitiator can be a free radical photo-initiator, a cationicphoto-initiator, or any combination thereof.

A free radical photoinitiator may be any compound that produces a freeradical upon exposure to radiation such as ultraviolet or visibleradiation and thereby initiates a polymerization reaction. Non-limitingexamples of suitable photoinitiators include phenyl ketones, such asalkyl/cycloalkyl phenyl ketones, benzophenones (aromatic ketones) suchas benzophenone, methyl benzophenone, Michler's ketone and xanthones;acylphosphine oxide type photo-initiators such as2,4,6-trimethylbenzolydiphenyl phosphine oxide (TMPO),2,4,6-trimethylbenzoylethoxyphenyl phosphine oxide (TEPO), andbisacylphosphine oxides (BAPO's); benzoins and benzoin alkyl ethers suchas benzoin, benzoin methyl ether and benzoin isopropyl ether and thelike. Examples of photoinitiators are alpha-amino ketone, and1-hydroxycyclohexyl phenyl ketone (e.g., marketed as Igracure® 184).

A free-radical photo-initiator may be used alone or in combination witha co-initiator. Co-initiators are used with initiators that need asecond molecule to produce a radical that is active in the UV-systems.Benzophenone is an example of a photoinitiator that requires a secondmolecule, such as an amine, to produce a curable radical. Afterabsorbing radiation, benzophenone reacts with a ternary amine byhydrogen abstraction, to generate an alpha-amino radical which initiatespolymerization of acrylates. Non-limiting example of a class ofco-initiators are alkanolamines such as triethylamine,methyldiethanolamine and triethanolamine.

Suitable cationic photoinitiators include, for example, compounds whichform aprotic acids or Bronstead acids upon exposure to ultravioletand/or visible light sufficient to initiate polymerization. Thephotoinitiator used may be a single compound, a mixture of two or moreactive compounds, or a combination of two or more different compounds,i.e. co-initiators. Non-limiting examples of suitable cationicphotoinitiators include aryldiazonium salts, diaryliodonium salts,triarylsulphonium salts, triarylselenonium salts and the like. Anexemplary cationic photoinitiator is a mixture of triarylsolfoniumhexafluoroantimonate salts.

In some of any of the embodiments described herein, the curableformulation may further comprise one or more additional agents that arebeneficially used in the fabrication process. Such agents include, forexample, surface active agents, inhibitors and stabilizers.

In some embodiments, a curable formulation as described herein comprisesa surface active agent. A surface-active agent may be used to reduce thesurface tension of the formulation to the value required for jetting orfor other printing process, which is typically around 30 dyne/cm. Anexemplary such agent is a silicone surface additive such as, but notlimited to, a surface agent marketed as BYK-345.

In some embodiments, a curable formulation as described herein furthercomprises an inhibitor, which inhibits pre-polymerization of the curablematerial during the fabrication process and before it is subjected tocuring conditions. An exemplary stabilizer (inhibitor) isTris(N-nitroso-N-phenylhydroxylamine) Aluminum Salt (NPAL) (e.g., asmarketed under FirstCure® NPAL).

Suitable stabilizers include, for example, thermal stabilizers, whichstabilize the formulation at high temperatures.

In some of any of the embodiments described herein, the curableformulation is devoid of a silicon polyether.

In some of any of the embodiments described herein, the curableformulation further comprises water.

In some of any of the embodiments described herein, a curableformulation comprises one or more curable materials, in addition to themono-functional and multi-functional curable materials described herein.

In some of any of the embodiments described herein, such curablematerials can be any curable materials commonly used in modelfabrication processes, for example, 3D printing processes.

In some of these embodiments, one or more of the additional curablematerials is a water-miscible curable material.

In some of any of these embodiments, the additional curable materialsare curable upon exposure to the same curing conditions as themono-functional and multi-functional curable materials described herein.For example, when the mono-functional and multi-functional curablematerials described herein, are photopolymerizable materials (e.g.,UV-curable), the one or more additional curable materials are alsophotopolymerizable (e.g., UV-curable).

The additional curable materials can be monomeric, oligomeric and/orpolymeric materials.

Exemplary additional mono-functional UV-curable materials include, butare not limited to, acryloyl morpholine (ACMO), hydroxyethyl acrylamide,hydroxymethyl acrylamide, N-(3,3-dimethylaminopropyl) methacrylamide,methacrylamide (2-methyl-propenamide), NIPAM, vinyl ethers, isobornylacrylate, isobornyl methacrylate, oligo(alkylene glycol) monoacrylates,and oligouerthane acrylates. Other water-miscible mono-functionalacrylates, methacrylates, acrylamides or methacrylamides arecontemplated.

Exemplary additional multi-functional (e.g., di-functional) UV-curablematerials include, but are not limited to, poly(ethylene glycol)diacrylates, poly(ethylene glycol) dimethacrylate, poly(ethyleneglycol)-poly(ethylene glycol) urethane diacrylates, and a partiallyacrylated polyol oligomers.

Exemplary Support Material Formulations:

In some of any of the embodiments described herein, a curable supportmaterial formulation as described herein comprises one or more of themono-functional curable materials presented in Table 1 below.

In some of any of the embodiments described herein, a curable supportmaterial formulation as described herein comprises one or more of themulti-functional curable materials presented in Table 2 below.

In some of any of the embodiments described herein, a curable supportmaterial formulation as described herein comprises one or more of themono-functional curable materials presented in Table 1 below and one ormore of the multi-functional curable materials presented in Table 2below.

In some of any of the embodiments described herein, a curableformulation comprises one or more mono-functional curable materialrepresented by Formula I, as described herein; and/or one or more of themulti-functional curable materials as described herein.

In some of any of the embodiments described herein, a curableformulation comprises one or more mono-functional curable materialrepresented by Formula I, as described herein; and/or one or more of themulti-functional curable materials represented by Formula II, asdescribed herein.

According to some of any of the embodiments described herein, thecurable formulation is such that a concentration of the mono-functionalcurable material(s) represented by Formula I as described herein rangesfrom 40% to 90%, or from 40% to 80%, or from 50% to 80%, by weight ofthe total weight of the formulation.

According to some of any of the embodiments described herein, thecurable formulation is such that a total concentration ofmono-functional curable materials (e.g., curable materials representedby Formula I as described herein and additional mono-functional curablematerials as described herein) ranges from 40% to 90%, or from 40% to80%, or from 50% to 80%, by weight of the total weight of theformulation, including any intermediate values and subrangestherebetween.

According to some of any of the embodiments described herein, thecurable formulation is such that a concentration of the multi-functionalcurable material as described herein is at least 5% by weight of thetotal weight of the formulation.

According to some of any of the embodiments described herein, thecurable formulation is such that a concentration of the multi-functionalcurable material as described herein ranges from 5 to 80, or from 5 to75, or from 5 to 70, or from 5 to 65, or from 5 to 60, or from 5 to 50,or from 5 to 40, or from 5 to 30, or from 5 to 30, or from 5-25, or from5-20, or from 5 to 15, weight percents of the total weight of theformulation, including any intermediate values and subrangestherebetween.

According to some of any of the embodiments described herein, thecurable formulation is such that a total concentration ofmulti-functional curable materials (a multi-functional curable materialas described herein ranges from 5 to 80, or from 5 to 75, or from 5 to70, or from 5 to 65, or from 5 to 60, or from 5 to 50, or from 5 to 40,or from 5 to 30, or from 5 to 30, or from 5 to 25, or from 5 to 20, orfrom 5 to 15, weight percents of the total weight of the formulation,including any intermediate values and subranges therebetween.

The following lists non-limiting examples of combinations ofmono-functional and multi-functional curable materials to be included ina curable formulation as described herein:

AM-130G and SR-610, at a DOC in a range of from 5 to 65;

AM-130G and SR-259, at a DOC in a range of from 5 to 90;

AM-130G and GDGDA, at a DOC in a range of from 5 to 65;

AM-130G and SR-508, at a DOC in a range of from 5 to 65;

AM-130G and SR-833S, at a DOC in a range of from 5 to 65;

AM-130G and SR-415, at a DOC in a range of from 5 to 25;

AM-130G and SR-444D, at a DOC in a range of from 5 to 65;

AM-130G and SR-368, at a DOC in a range of from 5 to 65;

AM-130G and SR-355, at a DOC in a range of from 5 to 65;

AM-130G and SR-399, at a DOC in a range of from 5 to 65;

HEAA and SR-610, at a DOC in a range of from 5 to 25;

HEAA and SR-259, at a DOC in a range of from 5 to 45;

HEAA and GDGDA, at a DOC in a range of from 5 to 45;

HEAA and SR-508, at a DOC in a range of from 5 to 25;

HEAA and SR-833S, at a DOC in a range of from 5 to 65;

HEAA and SR-415, at a DOC of 5;

HEAA and SR-444D, at a DOC in a range of from 5 to 45;

HEAA and SR-368, at a DOC in a range of from 5 to 25;

HEAA and SR-355, at a DOC in a range of from 5 to 25;

HEAA and SR-399, at a DOC in a range of from 5 to 25;

ACMO and SR-259, at a DOC of 5;

ACMO and SR-415, at a DOC of 5;

DMAPAA and SR-399, at a DOC of 25-45;

PEA-6 and SR-508, at a DOC of 5-65;

PEA-6 and SR-355, at a DOC of 5-65;

PEA-6 and SR-399, at a DOC of 5-65.

According to some of any of the embodiments described herein, thesupport curable formulation further comprises a non-curable material asdescribed herein. In some embodiments, a concentration of thenon-curable material ranges from 1 to 20, or from 1 to 10, weightpercents of the total weight of the formulation.

According to some of any of the embodiments described herein, thecurable formulation further comprises an initiator (e.g., aphotoinitiator) at a concentration of from 0.1 to 4, or from 0.5 to 4,or from 0.5 to 3, or from 0.5 to 2, weight percents of the total weightof the composition.

According to some of any of the embodiments described herein, thecurable formulation further comprises an inhibitor at a concentration offrom 0 to 2 weight percents of the total weight of the composition;and/or a surfactant, at a concentration of 0 to 2 weight percents of thetotal weight of the composition.

Exemplary formulations are presented in Tables 3-5 below.

According to some of any of the embodiments described herein, thecurable formulation exhibits a viscosity that is suitable for 3D inkjetprinting.

In exemplary embodiments, the viscosity of the curable formulation islower than 30 cps, or lower than 25 cps, or lower than 20 cps, at theworking temperature. In some embodiments, the viscosity of theformulation is higher at room temperature and can be, for example, above50 cps, or above 80 cps, at room temperature.

In some of any of the embodiments described herein, the curableformulation is such that exhibits a viscosity of from 10 to 20 cps atroom temperature. In some embodiments, the curable materials, and thenon-curable materials, and the concentration of each, are selected ormanipulated such that the formulation exhibits a desired viscosity asdescribed herein (before curing).

According to some of any of the embodiments described herein, thecurable formulation as described herein is curable upon exposure tolight energy.

According to some of any of the embodiments described herein, thecurable formulation as described herein is UV-curable, as definedherein, and is curable upon exposure to UV radiation.

Model Fabrication:

The curable formulation as described herein is suitable for use as anuncured building material formulation in additive manufacturing process,as defined herein.

The curable formulation as described herein is suitable for use as anuncured building material formulation in 3D-inkjet printing processes.

The curable formulation as described herein can be used in suchprocesses either as a modeling material formulation, for formingwater-breakable model objects, or as a support material formulation,which forms a cured support material that can be easily removed, asdescribed herein.

According to aspects of some of any of the embodiments described herein,there are provided methods of additive manufacturing, for fabricating athree-dimensional model object, which utilize a curable formulation asdescribed herein.

According to an aspect of some embodiments of the present invention,there is provided a method of fabricating a three-dimensional modelobject, which comprises dispensing a uncured building material so as tosequentially form a plurality of layers in a configured patterncorresponding to the shape of the object, wherein the building materialcomprises a curable formulation as described herein.

In some of any of the embodiments described herein, the uncured buildingmaterial comprises or consists of one or more modeling materialformulations, and one or more of these modeling material formulations isa curable formulation according to any one of the present embodiments.

In some of any of the embodiments described herein, the uncured buildingmaterial comprises one or more modeling material formulations, and oneor more support material formulations, and one or more of the supportmaterial formulations is a curable formulation according to any one ofthe present embodiments,

In some of any of the embodiments described herein, the method furthercomprises, subsequent to the dispensing, exposing the building materialto curing energy, to thereby obtain a printed objected which comprises acured modeling material and optionally a cured support material.

When an uncured building material comprises a curable formulation asdescribed herein as a support material formulation, the printed objectcomprises a cured modeling material and a cured support material, atleast some of which is a cured material formed of a curable formulationaccording to the present embodiments.

The method of fabricating a three-dimensional model object, whichutilizes a curable formulation as described herein is also referred toherein as a fabrication process or as a model fabrication process.

In some of any of the embodiments described herein for a method, inwhich the curable formulation as described herein is not a modelingmaterial formulation but rather a support material formulation, themodeling material formulation can be any modeling material formulationused in additive manufacturing such as 3D inkjet printing, and ispreferably curable under the same conditions at which the supportmaterial formulation is curable. The support material formulation is asdescribed herein in any of the respective embodiments and anycombination thereof.

According to some embodiments of the present invention, the fabricationmethod is additive manufacturing of a three-dimensional model object.

According to some of any embodiments of this aspect, formation of eachlayer is effected by dispensing at least one uncured building material,and exposing the dispensed building material to curing energy or curingconditions, as described herein, to thereby form a cured buildingmaterial, which is comprised of a cured modeling material and optionallya cured support material.

According to some of any of the embodiments described herein, theadditive manufacturing is preferably by three-dimensional (3D) inkjetprinting.

The method of the present embodiments manufactures three-dimensionalobjects in a layerwise manner by forming a plurality of layers in aconfigured pattern corresponding to the shape of the objects.

Each layer is formed by an additive manufacturing apparatus which scansa two-dimensional surface and patterns it. While scanning, the apparatusvisits a plurality of target locations on the two-dimensional layer orsurface, and decides, for each target location or a group of targetlocations, whether or not the target location or group of targetlocations is to be occupied by building material, and which type ofbuilding material (e.g., a modeling material formulation or a supportmaterial formulation) is to be delivered thereto. The decision is madeaccording to a computer image of the surface.

When the AM is by three-dimensional printing, an uncured buildingmaterial, as defined herein, is dispensed from a dispensing head havinga set of nozzles to deposit building material in layers on a supportingstructure. The AM apparatus thus dispenses building material in targetlocations which are to be occupied and leaves other target locationsvoid. The apparatus typically includes a plurality of dispensing heads,each of which can be configured to dispense a different buildingmaterial. Thus, different target locations can be occupied by differentbuilding materials (e.g., a modeling formulation and/or a supportformulation, as defined herein).

In some of any of the embodiments of this aspect of the presentinvention, the method begins by receiving 3D printing data correspondingto the shape of the object. The data can be received, for example, froma host computer which transmits digital data pertaining to fabricationinstructions based on computer object data, e.g., in a form of aStandard Tessellation Language (STL) or a StereoLithography Contour(SLC) format, Virtual Reality Modeling Language (VRML), AdditiveManufacturing File (AMF) format, Drawing Exchange Format (DXF), PolygonFile Format (PLY) or any other format suitable for Computer-Aided Design(CAD).

Next, droplets of the uncured building material as described herein aredispensed in layers, on a receiving medium, using at least two differentmulti-nozzle inkjet printing heads, according to the printing data. Thereceiving medium can be a tray of a three-dimensional inkjet system or apreviously deposited layer.

In some embodiments of the present invention, the dispensing is effectedunder ambient environment.

Optionally, before being dispensed, the uncured building material, or apart thereof (e.g., one or more formulations of the building material),is heated, prior to being dispensed. These embodiments are particularlyuseful for uncured building material formulations having relatively highviscosity at the operation temperature of the working chamber of a 3Dinkjet printing system. The heating of the formulation(s) is preferablyto a temperature that allows jetting the respective formulation througha nozzle of a printing head of a 3D inkjet printing system. In someembodiments of the present invention, the heating is to a temperature atwhich the respective formulation exhibits a viscosity of no more than Xcentipoises, where X is about 30 centipoises, preferably about 25centipoises and more preferably about 20 centipoises, or 18 centipoises,or 16 centipoises, or 14 centipoises, or 12 centipoises, or 10centipoises.

The heating can be executed before loading the respective formulationinto the printing head of the 3D printing system, or while theformulation is in the printing head or while the formulation passesthrough the nozzle of the printing head.

In some embodiments, the heating is executed before loading of therespective formulation into the printing head, so as to avoid cloggingof the printing head by the formulation in case its viscosity is toohigh.

In some embodiments, the heating is executed by heating the printingheads, at least while passing the formulation(s) through the nozzle ofthe printing head.

Once the uncured building material is dispensed on the receiving mediumaccording to the 3D printing data, the method optionally and preferablycontinues by exposing the dispensed building material to conditions thateffect curing. In some embodiments, the dispensed building material isexposed to curing energy by applying curing energy to the depositedlayers. Preferably, the curing is applied to each individual layerfollowing the deposition of the layer and prior to the deposition of theprevious layer.

The curing energy or condition can be, for example, a radiation, such asan ultraviolet or visible irradiation, or other electromagneticradiation, or electron beam radiation, depending on the buildingmaterial used. The curing energy or condition applied to the dispensedlayers serves for curing or solidifying or hardening the modelingmaterial formulation and/or the support material formulation.Preferably, the same curing energy or condition is applied to effectcuring of both the modeling materials and the support material, ifpresent. Alternatively, different curing energies or conditions areapplied to the dispensed building material, simultaneously orsequentially, to effect curing of the modeling material formulationand/or the support material formulation.

In some of any of the embodiments described herein, the method furthercomprises removing the cured support material, to thereby obtain thethree-dimensional model object.

When an uncured building material comprises a curable formulation asdescribed herein as a support material formulation, removing the curedsupport material formed of the curable formulation as described hereincomprises contacting the cured support material with water, or anaqueous solution

In some embodiments, removing the cured support material comprisescontacting the entire printed object with water or an aqueous solution.

In some embodiments, removing the cured support material is effected byimmersing the cured support material, or the entire printed object, inwater or an aqueous solution.

In some embodiments, the immersion is static immersion, namely, thewater or solution is not stirred.

Any volume of water or an aqueous solution can be used for removing acured support material as described herein. Since a cured supportmaterial as described herein physically decomposes upon immersion inwater, the concentration of the cured material in the water or solutiondoes not affect its decomposition time or rate.

In some of the embodiments where an aqueous solution is used, theaqueous solution is substantially neutral, namely, has a pH of 6-8, orof 7.

In some of the embodiments where an aqueous solution is used, theaqueous solution is neither an alkaline solution nor an acidic solution(such as solutions commonly used to dissolve cured support materials inadditive manufacturing).

The contacting with water or an aqueous solution can be effectedmanually or in an automated manner. Any system or apparatus usable forremoving a cured support material is contemplated.

In some of any of the embodiments described herein, the contacting iseffected for a time period that is suitable for a cured support materialat hand, and can range from few (e.g., 1-3) minutes, to several (e.g.,2-8) hours, as further described hereinabove.

In some embodiments, the contacting is effected without replacing thewater or aqueous solution (e.g., without introducing a fresh batch ofwater or aqueous solution to the apparatus or system where removal ofthe cured support material is performed).

Any system suitable for AM of an object (e.g., a model object) is usablefor executing the method as described herein.

A representative and non-limiting example of a system suitable for AM ofan object according to some embodiments of the present inventioncomprises an additive manufacturing apparatus having a dispensing unitwhich comprises a plurality of dispensing heads. Each head preferablycomprises an array of one or more nozzles, through which a liquid(uncured) building material is dispensed.

Preferably, but not obligatorily, the AM apparatus is athree-dimensional inkjet printing apparatus, in which case thedispensing heads are inkjet printing heads, and the building material isdispensed via inkjet technology. This need not necessarily be the case,since, for some applications, it may not be necessary for the additivemanufacturing apparatus to employ three-dimensional printing techniques.Representative examples of additive manufacturing apparatus contemplatedaccording to various exemplary embodiments of the present inventioninclude, without limitation, binder jet powder based apparatus, fuseddeposition modeling apparatus and fused material deposition apparatus.

Each dispensing head is optionally and preferably fed via one or morebuilding material reservoir(s) which may optionally include atemperature control unit (e.g., a temperature sensor and/or a heatingdevice), and a material level sensor. To dispense the building material,a voltage signal is applied to the dispensing heads to selectivelydeposit droplets of material via the dispensing head nozzles, forexample, as in piezoelectric inkjet printing technology. The dispensingrate of each head depends on the number of nozzles, the type of nozzlesand the applied voltage signal rate (frequency). Such dispensing headsare known to those skilled in the art of solid freeform fabrication.

Optionally, but not obligatorily, the overall number of dispensingnozzles or nozzle arrays is selected such that half of the dispensingnozzles are designated to dispense support material formulations (ifincluded in an uncured building material) and half of the dispensingnozzles are designated to dispense modeling material formulations, i.e.the number of nozzles jetting modeling materials is the same as thenumber of nozzles jetting support material. Yet it is to be understoodthat it is not intended to limit the scope of the present invention andthat the number of modeling material depositing heads (modeling heads)and the number of support material depositing heads (support heads) maydiffer. Generally, the number of modeling heads, the number of supportheads and the number of nozzles in each respective head or head arrayare selected such as to provide a predetermined ratio, a, between themaximal dispensing rate of the support material and the maximaldispensing rate of modeling material. The value of the predeterminedratio, a, is preferably selected to ensure that in each formed layer,the height of modeling material equals the height of support material.Typical values for a are from about 0.6 to about 1.5.

For example, for a=1, the overall dispensing rate of support materialformulation is generally the same as the overall dispensing rate of themodeling material formulation(s) when all modeling heads and supportheads operate.

In a preferred embodiment, there are M modeling heads each having marrays of p nozzles, and S support heads each having s arrays of qnozzles such that M×m×p=S×s×q. Each of the M×m modeling arrays and S×ssupport arrays can be manufactured as a separate physical unit, whichcan be assembled and disassembled from the group of arrays. In thisembodiment, each such array optionally and preferably comprises atemperature control unit and a material level sensor of its own, andreceives an individually controlled voltage for its operation.

The AM apparatus can further comprise a curing unit which can compriseone or more sources of a curing energy or a curing condition. The curingsource can be, for example, a radiation source, such as an ultravioletor visible or infrared lamp, or other sources of electromagneticradiation, or electron beam source, depending on the modeling materialformulation(s) being used. The curing energy source serves for curing orsolidifying the building material formulation(s).

The dispensing head and curing energy source (e.g., radiation source)are preferably mounted in a frame or block which is preferably operativeto reciprocally move over a tray, which serves as the working surface (areceiving medium). In some embodiments of the present invention, thecuring energy (e.g., radiation) sources are mounted in the block suchthat they follow in the wake of the dispensing heads to at leastpartially cure or solidify the materials just dispensed by thedispensing heads. According to the common conventions, the tray ispositioned in the X-Y plane, and is preferably configured to movevertically (along the Z direction), typically downward.

In various exemplary embodiments of the invention, the AM apparatusfurther comprises one or more leveling devices, e.g. a roller, whichserve to straighten, level and/or establish a thickness of the newlyformed layer prior to the formation of the successive layer thereon. Theleveling device preferably comprises a waste collection device forcollecting the excess material generated during leveling. The wastecollection device may comprise any mechanism that delivers the materialto a waste tank or waste cartridge.

In use, the dispensing heads as described herein move in a scanningdirection, which is referred to herein as the X direction, andselectively dispense building material in a predetermined configurationin the course of their passage over the tray. The building materialtypically comprises one or more types of support material formulationsand one or more types of modeling material formulations. The passage ofthe dispensing heads is followed by the curing of the modeling andsupport material formulation(s) by the source of curing energy orcondition (e.g., radiation). In the reverse passage of the heads, backto their starting point for the layer just deposited, an additionaldispensing of building material may be carried out, according topredetermined configuration. In the forward and/or reverse passages ofthe dispensing heads, the layer thus formed may be straightened by theleveling device, which preferably follows the path of the dispensingheads in their forward and/or reverse movement. Once the dispensingheads return to their starting point along the X direction, they maymove to another position along an indexing direction, referred to hereinas the Y direction, and continue to build the same layer by reciprocalmovement along the X direction. Alternatively, the dispensing heads maymove in the Y direction between forward and reverse movements or aftermore than one forward-reverse movement. The series of scans performed bythe dispensing heads to complete a single layer is referred to herein asa single scan cycle.

Once the layer is completed, the tray is lowered in the Z direction to apredetermined Z level, according to the desired thickness of the layersubsequently to be printed. The procedure is repeated to form athree-dimensional object which comprises a modeling material and asupport material in a layerwise manner.

In some embodiments, the tray may be displaced in the Z directionbetween forward and reverse passages of the dispensing head, within thelayer. Such Z displacement is carried out in order to cause contact ofthe leveling device with the surface in one direction and preventcontact in the other direction.

The system for performing the method as described herein optionally andpreferably comprises a building material supply apparatus whichcomprises the building material containers or cartridges and supplies aplurality of building material formulations (modeling materialformulation(s) and/or a support material formulation as describedherein) to the fabrication apparatus.

The system may further comprise a control unit which controls thefabrication apparatus and optionally and preferably also the supplyapparatus as described herein. The control unit preferably communicateswith a data processor which transmits digital data pertaining tofabrication instructions based on computer object data, stored on acomputer readable medium, preferably a non-transitory medium, in a formof a Standard Tessellation Language (STL) format or any other formatsuch as, but not limited to, the aforementioned formats. Typically, thecontrol unit controls the voltage applied to each dispensing head ornozzle array and the temperature of the building material in therespective printing head.

Once the manufacturing data is loaded to the control unit, it canoperate without user intervention. In some embodiments, the control unitreceives additional input from the operator, e.g., using a dataprocessor or using a user interface communicating with the control unit.The user interface can be of any type known in the art, such as, but notlimited to, a keyboard, a touch screen and the like. For example, thecontrol unit can receive, as additional input, one or more buildingmaterial types and/or attributes, such as, but not limited to, color,characteristic distortion and/or transition temperature, viscosity,electrical property, magnetic property. Other attributes and groups ofattributes are also contemplated.

Some embodiments contemplate the fabrication of an object by dispensingdifferent materials from different dispensing heads. These embodimentsprovide, inter alia, the ability to select materials from a given numberof materials and define desired combinations of the selected materialsand their properties. According to the present embodiments, the spatiallocations of the deposition of each material with the layer is defined,either to effect occupation of different three-dimensional spatiallocations by different materials, or to effect occupation ofsubstantially the same three-dimensional location or adjacentthree-dimensional locations by two or more different materials so as toallow post deposition spatial combination of the materials within thelayer, thereby to form a composite material at the respective locationor locations.

Any post deposition combination or mix of modeling materials iscontemplated. For example, once a certain material is dispensed it maypreserve its original properties. However, when it is dispensedsimultaneously with another modeling material or other dispensedmaterials which are dispensed at the same or nearby locations, acomposite material having a different property or properties to thedispensed materials is formed.

The present embodiments thus enable the deposition of a broad range ofmaterial combinations, and the fabrication of an object which mayconsist of multiple different combinations of materials, in differentparts of the object, according to the properties desired to characterizeeach part of the object.

Further details on the principles and operations of an AM system such asdescribed herein is found in U.S. patent application having PublicationNo. 2013/0073068, the contents of which are hereby incorporated byreference.

According to some embodiments of each of the methods and systemsdescribed herein, the uncured building material comprises at least onecurable formulation as described herein.

The Model Object:

According to an aspect of some embodiments of the present invention,there is provided a three-dimensional model object prepared by themethod as described herein, in any of the embodiments thereof and anycombination thereof.

According to an aspect of some embodiments of the present inventionthere is provided a 3D model object, fabricated by an AM method asdescribed herein.

According to an aspect of some embodiments of the present invention,there is provided a three-dimensional model object which is waterbreakable, or which comprises at least one water breakable portion, asdefined herein.

In some embodiments, such a model object is fabricated by a method asdescribed herein, in any one of the respective embodiments, wherein atleast one modeling material formulation used to form the model object isa curable formulation as described herein.

As used herein the term “about” refers to ±10%.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof. Throughout this application,various embodiments of this invention may be presented in a rangeformat. It should be understood that the description in range format ismerely for convenience and brevity and should not be construed as aninflexible limitation on the scope of the invention. Accordingly, thedescription of a range should be considered to have specificallydisclosed all the possible subranges as well as individual numericalvalues within that range. For example, description of a range such asfrom 1 to 6 should be considered to have specifically disclosedsubranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4,from 2 to 6, from 3 to 6 etc., as well as individual numbers within thatrange, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of thebreadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

As used herein the term “method” or “process” refers to manners, means,techniques and procedures for accomplishing a given task including, butnot limited to, those manners, means, techniques and procedures eitherknown to, or readily developed from known manners, means, techniques andprocedures by practitioners of, e.g., the chemical, mechanical, andcomputational arts.

Herein throughout, the term “water-miscible” describes a material whichis at least partially dissolvable or dispersible in water, that is, atleast 50% of the molecules move into the water upon mixture. This termencompasses the terms “water-soluble” and “water dispersible”.

Herein throughout, the term “water-soluble” describes a material thatwhen mixed with water in equal volumes or weights, a homogeneoussolution is formed.

Herein throughout, the term “water-dispersible” describes a materialthat forms a homogeneous dispersion when mixed with water in equalvolumes or weights.

Herein throughout, the phrase “linking moiety” or “linking group”describes a group that connects two or more moieties or groups in acompound. A linking moiety is typically derived from a bi- ortri-functional compound, and can be regarded as a bi- or tri-radicalmoiety, which is connected to two or three other moieties, via two orthree atoms thereof, respectively.

A linking moiety which is tri-functional or of higher functionality canbe branched moiety or a branching moiety, featuring 3 or more armsextending from the branching point.

Exemplary linking moieties include a linear or branched hydrocarbonmoiety or chain, optionally interrupted by one or more heteroatoms, asdefined herein, and/or any of the chemical groups listed below, whendefined as linking groups.

When a chemical group is referred to herein as “end group” it is to beinterpreted as a substituent, which is connected to another group viaone atom thereof.

As used herein, the term “amine” describes both a —NRxRy group and a—NRx- group, wherein Rx and Ry are each independently hydrogen, alkyl,cycloalkyl, aryl, as these terms are defined hereinbelow.

The amine group can therefore be a primary amine, where both Rx and Ryare hydrogen, a secondary amine, where Rx is hydrogen and Ry is alkyl,cycloalkyl or aryl, or a tertiary amine, where each of Rx and Ry isindependently alkyl, cycloalkyl or aryl.

Alternatively, Rx and Ry can each independently be hydroxyalkyl,trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl,heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate,hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano,nitro, azo, sulfonamide, carbonyl, C-carboxylate, O-carboxylate,N-thiocarbamate, O-thiocarbamate, urea, thiourea, N-carbamate,O-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine.

The term “amine” is used herein to describe a —NRxRy group in caseswhere the amine is an end group, as defined hereinunder, and is usedherein to describe a —NRx- group in cases where the amine is a linkinggroup or is or part of a linking moiety.

An amine end group can be a primary amine, in case both Rx and Ry arehydrogen, or secondary, when one of Rx and Ry is other than hydrogen(e.g., alkyl, cycloalkyl, aryl, alkenyl, and the like), or tertiary, incase each of Rx and Ry is other than hydrogen.

An amine linking group is a secondary amine when Rx is hydrogen, and isa tertiary amine when Rx is other than hydrogen.

The term “alkyl” describes a saturated aliphatic hydrocarbon includingstraight chain and branched chain groups. Preferably, the alkyl grouphas 1 to 20 carbon atoms. Whenever a numerical range; e.g., “1-20”, isstated herein, it implies that the group, in this case the alkyl group,may contain 1 carbon atom, 2 carbon atoms, 3 carbon atoms, etc., up toand including 20 carbon atoms. More preferably, the alkyl is a mediumsize alkyl having 1 to 10 carbon atoms. Most preferably, unlessotherwise indicated, the alkyl is a lower alkyl having 1 to 4 carbonatoms (C(1-4) alkyl). The alkyl group may be substituted orunsubstituted. Substituted alkyl may have one or more substituents,whereby each substituent group can independently be, for example,hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl,heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine.

The alkyl group can be an end group, as this phrase is definedhereinabove, wherein it is attached to a single adjacent atom, or alinking group, as this phrase is defined hereinabove, which connects twoor more moieties via at least two carbons in its chain. When the alkylis a linking group, it is also referred to herein as “alkylene” or“alkylene chain”.

Alkene and alkyne, as used herein, are an alkyl, as defined herein,which contains one or more double bond or triple bond, respectively.

The term “cycloalkyl” describes an all-carbon monocyclic ring or fusedrings (i.e., rings which share an adjacent pair of carbon atoms) groupwhere one or more of the rings does not have a completely conjugatedpi-electron system. Examples include, without limitation, cyclohexane,adamantine, norbornyl, isobornyl, and the like. The cycloalkyl group maybe substituted or unsubstituted. Substituted cycloalkyl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The cycloalkyl group can be an end group, as this phrase isdefined hereinabove, wherein it is attached to a single adjacent atom,or a linking group, as this phrase is defined hereinabove, connectingtwo or more moieties at two or more positions thereof.

The term “heteroalicyclic” describes a monocyclic or fused ring grouphaving in the ring(s) one or more atoms such as nitrogen, oxygen andsulfur. The rings may also have one or more double bonds. However, therings do not have a completely conjugated pi-electron system.Representative examples are piperidine, piperazine, tetrahydrofuran,tetrahydropyrane, morpholino, oxalidine, and the like. Theheteroalicyclic may be substituted or unsubstituted. Substitutedheteroalicyclic may have one or more substituents, whereby eachsubstituent group can independently be, for example, hydroxyalkyl,trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl,heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate,hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano,nitro, azo, sulfonamide, C-carboxylate, O-carboxylate, N-thiocarbamate,O-thiocarbamate, urea, thiourea, O-carbamate, N-carbamate, C-amide,N-amide, guanyl, guanidine and hydrazine. The heteroalicyclic group canbe an end group, as this phrase is defined hereinabove, where it isattached to a single adjacent atom, or a linking group, as this phraseis defined hereinabove, connecting two or more moieties at two or morepositions thereof.

The term “aryl” describes an all-carbon monocyclic or fused-ringpolycyclic (i.e., rings which share adjacent pairs of carbon atoms)groups having a completely conjugated pi-electron system. The aryl groupmay be substituted or unsubstituted. Substituted aryl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The aryl group can be an end group, as this term is definedhereinabove, wherein it is attached to a single adjacent atom, or alinking group, as this term is defined hereinabove, connecting two ormore moieties at two or more positions thereof.

The term “heteroaryl” describes a monocyclic or fused ring (i.e., ringswhich share an adjacent pair of atoms) group having in the ring(s) oneor more atoms, such as, for example, nitrogen, oxygen and sulfur and, inaddition, having a completely conjugated pi-electron system. Examples,without limitation, of heteroaryl groups include pyrrole, furan,thiophene, imidazole, oxazole, thiazole, pyrazole, pyridine, pyrimidine,quinoline, isoquinoline and purine. The heteroaryl group may besubstituted or unsubstituted. Substituted heteroaryl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,O-carbamate, N-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The heteroaryl group can be an end group, as this phrase isdefined hereinabove, where it is attached to a single adjacent atom, ora linking group, as this phrase is defined hereinabove, connecting twoor more moieties at two or more positions thereof. Representativeexamples are pyridine, pyrrole, oxazole, indole, purine and the like.

The term “halide” and “halo” describes fluorine, chlorine, bromine oriodine.

The term “haloalkyl” describes an alkyl group as defined above, furthersubstituted by one or more halide.

The term “sulfate” describes a —O—S(═O)₂—ORx end group, as this term isdefined hereinabove, or an —O—S(═O)₂—O— linking group, as these phrasesare defined hereinabove, where Rx is as defined hereinabove.

The term “thiosulfate” describes a —O—S(═S)(═O)—ORx end group or a —O—S(═S)(═O)—O— linking group, as these phrases are defined hereinabove,where Rx is as defined hereinabove.

The term “sulfite” describes an —O—S(═O)—O—Rx end group or a —O—S(═O)—O—group linking group, as these phrases are defined hereinabove, where Rx′is as defined hereinabove.

The term “thiosulfite” describes a —O—S(═S)—O—Rx end group or an—O—S(═S)—O— group linking group, as these phrases are definedhereinabove, where Rx is as defined hereinabove.

The term “sulfinate” describes a —S(═O)—ORx end group or an —S(═O)—O—group linking group, as these phrases are defined hereinabove, where Rxis as defined hereinabove.

The term “sulfoxide” or “sulfinyl” describes a —S(═O)Rx end group or an—S(═O)— linking group, as these phrases are defined hereinabove, whereRx is as defined hereinabove.

The term “sulfonate” describes a —S(═O)₂-Rx end group or an —S(═O)₂—linking group, as these phrases are defined hereinabove, where Rx is asdefined herein.

The term “S-sulfonamide” describes a —S(═O)₂—NRxRy end group or a—S(═O)₂—NRx- linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

The term “N-sulfonamide” describes an RxS(═O)₂—NRy- end group or a—S(═O)₂—NRx- linking group, as these phrases are defined hereinabove,where Rx and Ry are as defined herein.

The term “disulfide” refers to a —S—SRx end group or a —S—S— linkinggroup, as these phrases are defined hereinabove, where Rx is as definedherein.

The term “phosphonate” describes a —P(═O)(ORx)(ORy) end group or a—P(═O)(ORx)(O)— linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

The term “thiophosphonate” describes a —P(═S)(ORx)(ORy) end group or a—P(═S)(ORx)(O)— linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

The term “phosphinyl” describes a —PRxRy end group or a —PRx- linkinggroup, as these phrases are defined hereinabove, with Rx and Ry asdefined hereinabove.

The term “phosphine oxide” describes a —P(═O)(Rx)(Ry) end group or a—P(═O)(Rx)- linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

The term “phosphine sulfide” describes a —P(═S)(Rx)(Ry) end group or a—P(═S)(Rx)- linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

The term “phosphite” describes an —O—PRx(═O)(ORy) end group or an —O—PRx(═OXO)— linking group, as these phrases are defined hereinabove, withRx and Ry as defined herein.

The term “carbonyl” or “carbonate” as used herein, describes a —C(═O)—Rxend group or a —C(═O)— linking group, as these phrases are definedhereinabove, with Rx as defined herein.

The term “thiocarbonyl” as used herein, describes a —C(═S)—Rx end groupor a —C(═S)— linking group, as these phrases are defined hereinabove,with Rx as defined herein.

The term “oxo” as used herein, describes a (═O) group, wherein an oxygenatom is linked by a double bond to the atom (e.g., carbon atom) at theindicated position.

The term “thiooxo” as used herein, describes a (═S) group, wherein asulfur atom is linked by a double bond to the atom (e.g., carbon atom)at the indicated position.

The term “oxime” describes a ═N—OH end group or a ═N—O— linking group,as these phrases are defined hereinabove.

The term “hydroxyl” describes a —OH group.

The term “alkoxy” describes both an —O-alkyl and an —O-cycloalkyl group,as defined herein.

The term “aryloxy” describes both an —O-aryl and an —O-heteroaryl group,as defined herein.

The term “thiohydroxy” describes a —SH group.

The term “thioalkoxy” describes both a —S-alkyl group, and a—S-cycloalkyl group, as defined herein.

The term “thioaryloxy” describes both a —S-aryl and a —S-heteroarylgroup, as defined herein.

The “hydroxyalkyl” is also referred to herein as “alcohol”, anddescribes an alkyl, as defined herein, substituted by a hydroxy group.In some embodiments, the alkyl is substituted by hydroxy at a distalposition with respect to its attachment point.

The term “cyano” describes a —C≡N group.

The term “isocyanate” describes an —N═C═O group.

The term “isothiocyanate” describes an —N═C═S group.

The term “nitro” describes an —NO₂ group.

The term “acyl halide” describes a —(C═O)Rz group wherein Rz is halide,as defined hereinabove.

The term “azo” or “diazo” describes an —N═NRx end group or an —N═N—linking group, as these phrases are defined hereinabove, with Rx asdefined hereinabove.

The term “peroxo” describes an —O—ORx end group or an —O—O— linkinggroup, as these phrases are defined hereinabove, with Rx as definedhereinabove.

The term “carboxylate” as used herein encompasses C-carboxylate and O—carboxylate.

The term “C-carboxylate” describes a —C(═O)—ORx end group or a —C(═O)—O—linking group, as these phrases are defined hereinabove, where Rx is asdefined herein.

The term “O-carboxylate” describes a —OC(═O)Rx end group or a —OC(═O)—linking group, as these phrases are defined hereinabove, where Rx is asdefined herein.

A carboxylate can be linear or cyclic. When cyclic, Rx and the carbonatom are linked together to form a ring, in C-carboxylate, and thisgroup is also referred to as lactone. Alternatively, Rx and O are linkedtogether to form a ring in O-carboxylate. Cyclic carboxylates canfunction as a linking group, for example, when an atom in the formedring is linked to another group.

The term “thiocarboxylate” as used herein encompasses C-thiocarboxylateand O-thiocarboxylate.

The term “C-thiocarboxylate” describes a —C(═S)—ORx end group or a—C(═S)—O— linking group, as these phrases are defined hereinabove, whereRx is as defined herein.

The term “O-thiocarboxylate” describes a —OC(═S)Rx end group or a—OC(═S)— linking group, as these phrases are defined hereinabove, whereRx is as defined herein.

A thiocarboxylate can be linear or cyclic. When cyclic, Rx and thecarbon atom are linked together to form a ring, in C-thiocarboxylate,and this group is also referred to as thiolactone. Alternatively, Rx andO are linked together to form a ring in O— thiocarboxylate. Cyclicthiocarboxylates can function as a linking group, for example, when anatom in the formed ring is linked to another group.

The term “carbamate” as used herein encompasses N-carbamate and O—carbamate.

The term “N-carbamate” describes an RyOC(═O)—NRx- end group or a—OC(═O)-NRx- linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

The term “O-carbamate” describes an —OC(═O)—NRxRy end group or an—OC(═O)—NRx- linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

A carbamate can be linear or cyclic. When cyclic, Rx and the carbon atomare linked together to form a ring, in O-carbamate. Alternatively, Rxand O are linked together to form a ring in N-carbamate. Cycliccarbamates can function as a linking group, for example, when an atom inthe formed ring is linked to another group.

The term “carbamate” as used herein encompasses N-carbamate andO-carbamate.

The term “thiocarbamate” as used herein encompasses N-thiocarbamate andO-thiocarbamate.

The term “O-thiocarbamate” describes a —OC(═S)—NRxRy end group or a—OC(═S)—NRx- linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

The term “N-thiocarbamate” describes an RyOC(═S)NRx- end group or a—OC(═S)NRx- linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

Thiocarbamates can be linear or cyclic, as described herein forcarbamates.

The term “dithiocarbamate” as used herein encompasses S-dithiocarbamateand N-dithiocarbamate.

The term “S-dithiocarbamate” describes a —SC(═S)—NRxRy end group or a—SC(═S)NRx- linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

The term “N-dithiocarbamate” describes an RySC(═S)NRx- end group or a—SC(═S)NRx- linking group, as these phrases are defined hereinabove,with Rx and Ry as defined herein.

The term “urea”, which is also referred to herein as “ureido”, describesa —NRxC(═O)—NRyRq end group or a —NRxC(═O)—NRy- linking group, as thesephrases are defined hereinabove, where Rz and Ry are as defined hereinand Rq is as defined herein for Rx and Ry.

The term “thiourea”, which is also referred to herein as “thioureido”,describes a —NRx-C(═S)—NRyRq end group or a —NRx-C(═S)—NRy- linkinggroup, with Rx, Ry and Rq as defined herein.

The term “amide” as used herein encompasses C-amide and N-amide.

The term “C-amide” describes a —C(═O)—NRxRy end group or a —C(═O)-NRx-linking group, as these phrases are defined hereinabove, where Rx and Ryare as defined herein.

The term “N-amide” describes a RxC(═O)—NRy- end group or aRxC(═O)—N—linking group, as these phrases are defined hereinabove, whereRx and Ry are as defined herein.

An amide can be linear or cyclic. When cyclic, Rx and the carbon atomare linked together to form a ring, in C-amide, and this group is alsoreferred to as lactam. Cyclic amides can function as a linking group,for example, when an atom in the formed ring is linked to another group.

The term “guanyl” describes a RxRyNC(═N)— end group or a -RxNC(═N)—linking group, as these phrases are defined hereinabove, where Rx and Ryare as defined herein.

The term “guanidine” describes a -RxNC(═N)—NRyRq end group or a—RxNC(═N)—NRy- linking group, as these phrases are defined hereinabove,where Rx, Ry and Rq are as defined herein.

The term “hydrazine” describes a —NRx-NRyRq end group or a —NRx-NRy-linking group, as these phrases are defined hereinabove, with Rx, Ry,and Rq as defined herein.

As used herein, the term “hydrazide” describes a —C(═O)—NRx-NRyRq endgroup or a —C(═O)—NRx-NRy- linking group, as these phrases are definedhereinabove, where Rx, Ry and Rq are as defined herein.

As used herein, the term “thiohydrazide” describes a —C(═S)—NRx-NRyRqend group or a —C(═S)—NRx-NRy- linking group, as these phrases aredefined hereinabove, where Rx, Ry and Rq are as defined herein.

Herein, the term “hydrocarbon” describes an organic moiety thatincludes, as its basic skeleton, a chain of carbon atoms, also referredto herein as a backbone chain, substituted mainly by hydrogen atoms. Thehydrocarbon can be saturated or unsaturated, linear or branched, and canbe comprised of aliphatic, alicyclic and/or aromatic moieties, and canoptionally be substituted by one or more substituents (other thanhydrogen).

The hydrocarbon moiety can optionally be interrupted by one or moreheteroatoms, including, without limitation, one or more oxygen, nitrogen(substituted or unsubstituted, as defined herein for —NR₁— or for anamine linking group) and/or sulfur atoms.

The number of carbon atoms in a hydrocarbon moiety can range from 2 to20, and is preferably lower, e.g., from 1 to 10, or from 1 to 6, or from1 to 4. A hydrocarbon can be a linking group or an end group.

In some embodiments of any of the embodiments described herein relatingto a hydrocarbon, the hydrocarbon is not interrupted by any heteroatom,nor does it comprise heteroatoms in its backbone chain, and can be analkylene chain, or be comprised of alkyls, cycloalkyls, aryls, alkaryls,aralkyls, alkenes and/or alkynes, as defined herein, covalently attachedto one another in any order.

In some of these embodiments, the hydrocarbon is an alkylene chain.

The term “alkylene” describes a saturated aliphatic hydrocarbon group,as this term is defined herein. This term is also referred to herein as“alkyl”.

The alkylene can be substituted or unsubstituted, as defined herein foralkyl.

In some embodiments, when a hydrocarbon as described herein isinterrupted by one or more heteroatoms, the hydrocarbon can comprisesone or more alkylene glycol groups (units).

As used herein, the term “alkylene glycol” describes a—[(CRxRy)_(z)-O]_(y)-Rq end group or a -[(CRxRy)_(z)-O]_(y)— linkinggroup, with Rx, Ry and Rq being as defined herein, and with z being aninteger of from 1 to 10, preferably, 2-6, more preferably 2 or 3, and ybeing an integer of 1 or more. Preferably Rx and Ry are both hydrogen.When z is 2 and y is 1, this group is ethylene glycol. When z is 3 and yis 1, this group is propylene glycol.

When y is greater than 4, the alkylene glycol is referred to herein aspoly(alkylene glycol). In some embodiments of the present invention, apoly(alkylene glycol) group or moiety can have from 1 to 20 repeatingalkylene glycol units, such that z is 1 to 20, preferably 1-10, morepreferably 1-8, or as further defined hereinabove.

In some embodiments, a hydrocarbon moiety as described herein is apoly(alkylene glycol) moiety.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Various embodiments and aspects of the present invention as delineatedhereinabove and as claimed in the claims section below find experimentalsupport in the following examples.

EXAMPLES

Reference is now made to the following examples, which together with theabove descriptions illustrate some embodiments of the invention in a nonlimiting fashion.

Example 1 Exemplary Mono-Functional and Multi-Functional CurableMaterials

Table 1 below presents exemplary hydrophilic mono-functional curablematerials that were used for forming the tested formulations.

TABLE 1 Chemical/Commercial name Cas No. Structure (3-Acrylamidopropyl)trimethylammonium chloride (DMAPAA-Q) 45021-77-0

N-[3-(Dimethylamino) propyl]acrylamide (DMAPAA)  3845-76-9

N,N-Dimethylacrylamide (DMAA)  2680-03-7

N,N-Diethylacrylamide (DEAA)  2675-94-7

SR256 Di(ethylene glycol) ethyl ether acrylate (EOEOEA)  7328-17-8

SR550 Poly(ethylene glycol) methyl ether methacrylate (MPEG350A)26915-72-0

SR551 Poly(ethylene glycol) methyl ether acrylate (MPEG350A) 32171-39-4

[2-(acyloyloxy)ethyl] trimethylammonium chloride (Adamquat MC 80)44992-01-0

3- Trimethylammoniumpropyl methacrylamide chloride (aq. Solution)(MAPTAC) 51410-72-1

2-Trimethylammoniumethyl methacrylate chloride (aq. Solution) (TMAEMC) 5039-78-1

Polyethylene glycol (6) monoacrylate MPEG260 LD 32171-39-4

Acryloyl morpholine (ACMO ™)  5117-12-4

2-Hydroxyethyl acrylate (HEA)  818-61-1

Ethoxylated O- phenylphenol acrylate (A-LEN-10) 72009-86-0

Methoxy Polyethylene Glycol 400 Acrylate (EO 9 mol) (AM-90G) 32171-39-4

Methoxy Polyethylene Glycol 550 Acrylate (EO 13 mol) (AM-130G)32171-39-4

Polyethylene Glycol phenyl ether acrylate (AM-20GY) 56641-05-5

N-Hydroxyethyl acrylamide (HEAA)  7646-67-5

Polyethylene glycol (6) monoacrylate (PEA-6) 26403-58-7

Vinyl Phosphonic Acid (85% wt. in H₂O)  1746-03-8

Acrylic Acid   79-10-7

Table 2 below presents exemplary multi-functional curable materials thatwere used for forming the tested formulations.

TABLE 2 Chemical/ Commercial name Cas No. Structure N,N′- Methylenebis(acrylamide) (MBA)  110-26-9

3-(Acryloyloxy)-2- hydroxypropyl methacrylate (AMAHP)  1709-71-3

SR444D Pentaerythritol triacrylate (PETIA)  3524-68-3

SR368 Tris (2- hydroxyethyl) isocyanuratie triacrylate (THEICTA)40220-08-4

Glycerol 1,3- diglycerolate diacrylate (GDGDA) 60453-84-1

SR355 Di- Trimethylolpropane tetraacrylate (DiTMPTTA) 94108-97-1

SR259 Polyethylene glycol (200) diacrylate (PEG200DA) 26570-48-9

SR610 Polyethylene glycol (600) diacrylate (PEG600DA) 26570-48-9

SR833S Tricyclodecane dimethanol diacrylate (TCDDMDA) 42594-17-2

SR508 Dipropylene glycol diacrylate (DPGDA) 57472-68-1

SR415 Ethoxylated (20) trimethylolpropane triacrylate (TMP20EOTA)28961-43-5

SR399 Di-Pentaerythritol Pentaacrylate (DiPEPA) 60506-81-2

Example 2 Breakability Measurements

Procedure I (Molds):

Formulations comprising various combinations of one or moremono-functional curable material(s), one or more multi-functionalcurable material(s), and optionally one or more non-curablecomponent(s), as presented in Table 3 below, were prepared by mixing allcomponents, in the presence of a photoinitiator and optionally otheradditives, as described herein, at room temperature, optionally byheating in an oven at 50-85° C., for achieving homogeneity and fordegassing. The formulations were placed in a rectangular shaped mold, 63mm (x)×12.7 mm (y)×3.2 mm (z) dimensions (about 3 grams of eachformulation), and subjected to UV irradiation for a period of about 120minutes. The obtained cured material was then immersed in tap water (100mL) at room temperature, without stirring, and the time period betweent=0, immersion of the sample in water, to the time point at which allthe cured material breaks (which is equal to a cleaning time asdescribed herein) was recorded.

Procedure II (3D-Printed Objects):

Formulations comprising various combinations of one or moremono-functional curable material(s), one or more multi-functionalcurable material(s), and optionally one or more non-curablecomponent(s), as presented in Table 4 below, a photoinitiator andoptionally other additives, as described herein, were prepared by mixingall the components at room temperature, and optionally heating themixture in an oven at 50-85° C. The obtained formulations were used toprint, in matte, a 50-mm size owl, using, for example, CeroClear as amodel material, and a bounding box size of 50 mm×23 mm×25.8 mm, about 15grams, of a support material), as exemplified in FIG. 2A, on a Connex500and Objet3Connex system. The printed object was then immersed in a 3L-glass filled with tap water and cleaning times were recorded. Cleaningtime is measured from t=0, immersion of the printed object in water,until reaction reaches to an end (complete removal of the cured supportmaterial from the owl's surface). FIG. 2A presents the owl object uponcleaning.

For comparison, reference support formulations, which are made fromcurable materials other than those described herein, were used to printthe same owl object and the cleaning time was measured, according to theprocedure described hereinabove.

Results:

The data obtained in the mold experiments clearly show that almost alltested formulations decompose by breaking into small pieces upon staticimmersion in water in less than 2 hours.

The data obtained in the 3D-printing experiments is presented in Table 3below. These data further support the efficient decomposition of theformulations described herein upon immersion in water.

FIG. 2B presents comparative data of two reference formulations, denotedas Type 1 and Type 2 Support Reference formulations, and twoformulations according to exemplary embodiments of the presentinvention, as shown in Tables 4 and 5 below, respectively.

TABLE 4 (Type 1 formulation) Component Wt % A positively charged 50-80monoacrylate Hydroxy Acryl amide  5-20 A difunctional acrylate  5-15 aphotoinitiator 0.5-2.0

TABLE 5 (Type 2 formulation) Component Wt % MPEG monoacrylate 50-80 trifunctional acrylate 5-15 Polyol 5-15 alkyl diol 5-10 a photoinitiator0.5-2.0 

Type I formulation comprises, as an exemplary mono-functional curablematerial, a positively charged monoacrylate, and Type II formulationcomprises, as an exemplary mono-functional monomer, an alkoxy-terminatedalkylene glycol methacrylate. As shown in FIG. 2B, the formulationsdescribed herein supersede other support formulations.

TABLE 3 Mono-functional curable material(s) Multi-functional curablematerial(s) Non-curable material(s) Chemical % Chemical % Chemical %Chemical % Chemical % Chemical % Time substance wt. substance wtsubstance wt. substance wt. substance wt. substance wt. (min.) MPEG-40-60 Multifunctional 5-10 Polyol 10-40 100-200 mono- acrylate acrylateMPEG- 50-70 Urethane 5-10 Multifunctional 5-10 Polyol 10-20 Alkyl  3-10 60-100 mono- monoacrylate acrylate diol acrylate oligomer MPEG- 20-30Acryl 0-3  MPEG- 20-30 Multifunctional 5-10 Polyol 20-40  70-120 mono-amide mono meth- acrylate acrylate acrylate Charged 55-85 Hydroxy 0-10Cyclic  0-30 Di-functional 10-40  H₂O 0-5 30-60 mono- Acryl Acrylacrylate acrylate amide Amide Charged 30-50 Di-functional 10-20  H₂O +3-5 Alkyl 20-40 40-70 mono- acrylate Polyol 3-5 diol acrylate

Example 3 Water Absorption Measurements

Samples made of formulations containing various combinations ofmono-functional and multi-functional curable materials as describedherein (see, for example Tables 1 and 2 herein), were prepared in moldsas described in Example 2 hereinabove, using a rectangular flat mold40×40 mm and 3-5 mm thickness.

Cured samples were immersed in water (100 ml) for a time period of 48-72hours. Samples broke into particles, and following measurements weremade on the particles.

Using Filter Discs (MUNKTELL, Grade 1289) of 12 micron pore size, theparticles obtained upon breakage were collected from the water, and, toensure removal of water between particles, a vacuum pump with Buchnerfunnel was used.

The particles were weighted on a calibrated analytical scale, and werethereafter left to dry under ambient conditions for 96 hours.

The obtained dry particles were thereafter weighted on a calibratedanalytical scale.

The water absorption ratio was defined as the weight % differencecompared to the original weight of the samples (i) upon immersion inwater; and (ii) upon immersion in water and drying.

The data obtained for various formulations of AM-130G and SR-399, eachhaving a different degree of cross-linking (DOC) calculatedtheoretically as described hereinabove, is presented in Table 6 below.

It is noted that cured materials obtained from formulations containingnon-reactive (non-curable) materials lose weight after immersion inwater due to leaching of the non-reactive component.

TABLE 6 water AM- uptake wt % water 130G SR399 Degree of after uptake wt% (wt %) (wt %) Crosslinking immersion after drying Comment 99 1 6.51%349% 98% Swells 95 5 26.6% 125% 28% breakable 90 10 43.4% 90% −5% 85 1554.9% 87% 3% 80 20 63.3% 45% −1% 75 25 69.7% 31% −1% 50 50 87.3% 6% −3%Does not break

Example 4 Particles Size Measurements

Samples are prepared in mold, as described in Example 3 hereinabove, orby 3D inkjet printing, as described in Example 2 hereinabove.

The obtained samples were immersed in 100 ml water for a time period offrom 48 hours to 96 hours.

Using Filter Discs (MUNKTELL, Grade 1289) of 12 micron pore size, theparticles obtained upon breakage were collected from the water, and wereleft to dry under ambient conditions for a time period of at least 72hours. Particles were then weighted on a calibrated analytical scale.

For particles size measurements, five different Mesh sizes were used ina single test, arranged from 4 mm mesh size to 250 microns(4-2-1-0.5-0.25)

Particles were dispersed above the largest mesh, and the mesh column wasshaked to avoid particles settling due to clogging. Particles werecollected from each mesh by flipping into a fabric/aluminum foil, andweighted. Each weight fraction was then divided by the total weight.

It is noted that some variations occurred due to weight loss and/orcontamination during measurements.

The obtained data is presented in FIGS. 3A-C, for printed samples madeof AG-130G and SR368 (FIG. 3A), SR355 (FIG. 3B) and SR399 (FIG. 3C), forvarious degrees of crosslinking, and in FIGS. 4A-B for mold preparationsof AG-130G and SR399 (FIG. 4A) and of DMAPAA-Q and SR444D (FIG. 4B).

Table 7 below presents the weight percents of each component (mMo forthe mono-functional curable material; mCL for the multi-functionalcurable material), the molar ratio therebetween (nMo/CL) and therespective DOC.

TABLE 7 DOC Mo CL mMo (wt %) mCL (wt %) n [Mo/CL] (%) AM-130 SR-39997.30% 0.74% 104.50 5 AM-130 SR-399 93.52% 4.52% 16.50 25 AM-130 SR-39987.64% 10.40% 6.72 45 AM-130 SR-399 77.23% 20.81% 2.96 65 AM-130 SR-35597.10% 0.94% 76.00 5 AM-130 SR-355 92.40% 5.64% 12.00 25 AM-130 SR-35585.26% 12.78% 4.89 45 AM-130 SR-355 73.16% 24.88% 2.15 65 AM-130 SR-36896.95% 1.09% 57.00 5 AM-130 SR-368 91.50% 6.54% 9.00 25 AM-130 SR-36883.41% 14.62% 3.67 45 AM-130 SR-368 70.13% 27.91% 1.62 65 AM-130 SR-444D97.38% 0.66% 66.50 5 AM-130 SR-444D 93.99% 4.05% 10.50 25 AM-130 SR-444D88.65% 9.39% 4.28 45 AM-130 SR-444D 79.04% 18.99% 1.88 65 AM-130 SR-833S96.86% 1.18% 38.00 5 AM-130 SR-833S 91.03% 7.01% 6.00 25 AM-130 SR-833S82.46% 15.58% 2.44 45 AM-130 SR-833S 68.61% 29.43% 1.08 65 AM-130 SR-50897.06% 0.98% 38.00 5 AM-130 SR-508 92.16% 5.88% 6.00 25 AM-130 SR-50884.76% 13.28% 2.44 45 AM-130 SR-508 72.32% 25.72% 1.08 65 AM-130 GDGDA96.69% 1.35% 38.00 5 AM-130 GDGDA 90.10% 7.94% 6.00 25 AM-130 GDGDA80.60% 17.44% 2.44 45 AM-130 GDGDA 65.75% 32.29% 1.08 65 AM-130 SR-41595.06% 2.98% 57.00 5 AM-130 SR-415 81.80% 16.24% 9.00 25 AM-130 SR-41565.91% 32.13% 3.67 45 AM-130 SR-415 46.54% 51.50% 1.62 65 AM-130 SR-61095.27% 2.77% 38.00 5 AM-130 SR-610 82.81% 15.23% 6.00 25 AM-130 SR-61067.55% 30.49% 2.44 45 AM-130 SR-610 48.43% 49.61% 1.08 65 AM-130 SR-25996.87% 1.17% 38.00 5 AM-130 SR-259 91.07% 6.97% 6.00 25 AM-130 SR-25982.54% 15.50% 2.44 45 AM-130 SR-259 68.74% 29.30% 1.08 65

As shown, at degree of crosslinking higher than 10%, or higher than 20%,e.g., from 40 to about 70%, most particles have a size lower than 4 mm,and more than 50% of the particles have a size of 2 mm or less.

These data further show that by selecting a combination of amono-functional curable material and a multi-functional curable materialand the molar ratio therebetween, a degree of cross-linking can bedetermined. The degree of cross linking determined the particles sizedistribution, such that by manipulating parameters that affect the DOC,the particles size distribution obtained upon breakage of the curedmaterial can be pre-determined.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

1-64. (canceled)
 65. A curable formulation comprising at least onemono-functional curable material and at least one multi-functionalcurable material, said mono-functional and multi-functional curablematerials and a concentration ratio thereof being selected such that acured material formed upon exposing the formulation to a curing energybreaks into particles upon immersion in an aqueous solution, wherein:said cured material breaks upon said immersion into particles having asize ranging from 1 micron to 100 mm; and/or said cured materialfeatures a degree of cross linking that ranges from 10 to 80, or from 20to 70%; and/or said cured material is characterized by swelling capacityof from 10 to 300, or from 10 to 200, or from 10 to 150, or from 20 to150% by weight; and/or a 3-gram cube made of said cured material breaksupon static immersion in water in less than 10 hours, or less than 8hours, or less than 6 hours, or less than 4 hours, or less than 3 hours,or less than 2 hours, or less than 1 hour.
 66. The curable formulationof claim 65, wherein said at least one mono-functional curable monomeris represented by Formula I:

wherein: Ra is hydrogen, alkyl or cycloalkyl; and Z is represented byX-L-Y, wherein: X is selected from C(═O), C(═O)—NR₁, C(═O)—O,P(═O)—(OR₂)—O or is absent; Y is selected from O⁻M⁺, OR₃, NR₄R₅ orN⁺R₄R₅R₆Q⁻; L is a hydrocarbon moiety of 1 to 40 atoms in length,optionally interrupted by one or more heteroatom(s), said heteroatomsbeing independently selected from O, S and NR₂, or is absent; Q⁻ is anegatively charged counter ion; M⁺ is a positively charged counter ion;R₁ and R₂ are each independently selected from hydrogen, alkyl andcycloalkyl; R₃ is selected from hydrogen, alkyl, cycloalkyl and aryl;and R₄, R₅ and R₆ are each independently selected from hydrogen, alkyland cycloalkyl, or, alternatively, R₄ and R₅ form a cyclic ring.
 67. Thecurable formulation of claim 66, wherein Y is N⁺R₄R₅R₆Q.
 68. The curableformulation of claim 67, wherein L is a hydrocarbon moiety of 1 to 4carbon atoms in length.
 69. The curable formulation of claim 66, whereinY is NR₄R₅.
 70. The curable formulation of claim 66, wherein Y is OR₃.71. The curable formulation of claim 70, wherein L is a hydrocarbonmoiety interrupted by one or more heteroatom(s).
 72. The curableformulation of claim 65, wherein said mono-functional curable materialis characterized as forming a polymeric (cured) material, said polymericmaterial featuring: a water uptake of at least 200%; and/or ahydrophilic lipophilic balance, determined according to Davies method,of at least 10; and/or a water solubility of at least 50 weightpercents.
 73. The curable formulation of claim 65, wherein said at leastone multi-functional curable material is: (i) characterized as forming apolymer featuring a Tg higher than 20° C.; and/or (iii) is representedby Formula II:

wherein: Rb is hydrogen, alkyl or cycloalkyl; n is an integer of from 2to 10, representing a number of polymerizable groups —C(Rb)—W—; W ineach of said polymerizable groups is independently selected fromC(═O)—O, C(═O)—NR₈, and C(═O) or is absent; and B is a hydrocarbonmoiety of 1 to 20 atoms, interrupted and/or substituted by at least onehydrogen donor-containing group.
 74. The curable formulation of claim73, wherein said multi-functional curable material is characterized asforming a polymer featuring said Tg higher than 20° C., or higher than30° C., or higher than 50° C., or higher than 80° C.
 75. The curableformulation of claim 74, wherein said multi-functional curable materialis represented by Formula II.
 76. The curable formulation of claim 75,wherein said hydrogen donor-containing group is selected from oxygen,hydroxy, hydroxyalkyl, amine, aminoalkyl, thiol, thioalkyl.
 77. Thecurable formulation of claim 65, wherein a concentration of said atleast one mono-functional curable material ranges from 40 to 90, or from40 to 80, weight percents of the total weight of the formulation. 78.The curable formulation of claim 65, wherein a concentration of saidmulti-functional curable material ranges from 5 to 60 weight percents ofthe total weight of the formulation.
 79. The curable formulation ofclaim 65, further comprising at least one non-curable material.
 80. Thecurable formulation of claim 79, wherein said at least one non-curablematerial comprises a water-miscible polymer.
 81. The curable formulationof claim 65, wherein at least 50% of said particles have a size lowerthan 10 mm.
 82. A method of fabricating a three-dimensional modelobject, the method comprising dispensing a building material so as tosequentially form a plurality of layers in a configured patterncorresponding to the shape of the object, wherein said building materialcomprises the curable formulation of claim
 65. 83. The method of claim82, wherein said building material comprises a modeling materialformulation and a support material formulation, said support materialformulation comprising said curable formulation.
 84. The method of claim83, further comprising, subsequent to said dispensing, exposing thebuilding material to curing energy, to thereby obtain a printed objectedwhich comprises a cured support material formed of said curableformulation; and removing said cured support material, to thereby obtainthe three-dimensional model object, said removing comprises contactingsaid cured support material with water.
 85. The method of claim 84,wherein said contacting comprises static immersion of said cured supportmaterial in said water.